Capsules are not one uniform dosage form. A product developer may choose between a two-piece hard capsule and a one-piece softgel, then select a shell material, capsule size, fill format, release profile and manufacturing process. Each decision affects formulation compatibility, equipment requirements, production cost and the finished product’s performance.
Quick answer: the two primary structural types of capsules are hard capsules and soft capsules, or softgels. Hard capsules use a prefabricated cap-and-body shell and are commonly filled with powders, granules, pellets, mini-tablets or suitable non-aqueous liquids. Softgels are formed, filled and sealed in one continuous process and are mainly used for oils, solutions, suspensions and certain semi-solid fills. Both formats can use different shell materials and may be designed for immediate, delayed or modified release.
This guide classifies the different types of capsules by structure, shell material, contents, release behavior, size and application. It also connects each capsule type with the machinery required to manufacture it, helping pharmaceutical and supplement producers move from product concept to a practical production process.
How Are Capsules Classified?
Confusion arises when structure, material and drug-release behavior are mixed into one list. “HPMC capsule,” “hard capsule” and “enteric capsule” describe three different dimensions: material, physical construction and release function. One capsule may belong to all three categories at once—for example, a two-piece hard HPMC capsule engineered for delayed release.
A clearer classification uses five questions:
- What is its structure? Hard two-piece capsule, softgel or another specialized format.
- What is the shell made from? Gelatin, HPMC, pullulan, starch-based or another validated polymer system.
- What does it contain? Powder, granules, pellets, mini-tablets, liquid, suspension or semi-solid material.
- How should it release the contents? Immediate, delayed, enteric, extended or another modified-release profile.
- How is it manufactured? Shell filling and closing, liquid filling and sealing, or simultaneous forming, filling and sealing.
| Capsule Type | Physical Structure | Typical Contents | Common Shell Options | Main Manufacturing Route |
|---|---|---|---|---|
| Hard capsule | Rigid, two-piece cap and body | Powder, granules, pellets, beads, mini-tablets | Gelatin, HPMC, pullulan and specialty polymers | Fill a prefabricated body, then close or lock the cap |
| Liquid-filled hard capsule | Rigid, two-piece shell that is sealed after filling | Suitable non-aqueous liquids and semi-solids | Gelatin or selected non-gelatin shells | Liquid dosing followed by banding or another validated seal |
| Softgel | Flexible, one-piece shell with a formed seam | Oils, solutions, suspensions, pastes and semi-solids | Plasticized gelatin or validated plant-based systems | Shell formation, dosing and sealing occur together |
| Delayed/enteric capsule | May be hard or soft, depending on the technology | Acid-sensitive or intestinal-targeted formulations | Functional shell or applied coating | Use a functional shell or add a validated coating stage |
| Extended-release capsule | Usually a hard shell containing a release-control system | Coated pellets, beads, granules, matrices or mini-tablets | Often gelatin or HPMC hard shells | Fill pre-engineered modified-release components |
1. Hard Capsules
Best suited to powders, granules, pellets and combination fills
Hard capsules are rigid, prefabricated shells made as two separate pieces: a longer body and a shorter cap. During filling, the machine separates the cap from the body, doses the formulation into the body, replaces the cap and locks the two components together.
They are commonly called hard gelatin capsules, but not every hard capsule contains gelatin. HPMC, pullulan and other non-gelatin systems are also available. “Two-piece capsule” is therefore the more material-neutral description.
What can hard capsules contain?
- Free-flowing pharmaceutical or nutraceutical powders
- Granules produced to improve flow or dosing behavior
- Coated or uncoated pellets and multiparticulates
- Small tablets or combinations of tablets and pellets
- Powder-plus-pellet and pellet-plus-pellet combinations
- Selected non-aqueous liquids or semi-solids when the shell is compatible and properly sealed
Hard capsules provide considerable formulation flexibility. A manufacturer can change the capsule size, dosing system or internal components without adopting the entire preparation and drying process required for softgels. For a complete explanation of shell production and filling, see how capsules are made.
Advantages of hard capsules
- Broad compatibility with dry fill formats
- Multiple capsule sizes and color combinations
- Relatively straightforward product changeover
- Ability to combine ingredients with different release behaviors
- Commercial filling from laboratory to high-speed production
- Gelatin and vegetarian shell options
Limitations of hard capsules
Shells are sensitive to their storage environment. Excessively dry conditions can increase brittleness, while high humidity may soften or deform some shells. Static, powder flow, bulk density and capsule dimensional variation can also affect high-speed filling. A suitable capsule must therefore be evaluated as part of the complete formulation-machine system, not as an isolated container.
2. Softgel Capsules
Best suited to oils, non-aqueous solutions, suspensions and suitable semi-solids
A softgel is a flexible, one-piece capsule formed around its contents. In the common rotary-die process, two continuous shell ribbons enter a pair of rotating dies. A dosing pump delivers the fill through a heated wedge as the dies form, fill, seal and cut each capsule.
Traditional softgel shells contain gelatin, water and a plasticizer such as glycerol or sorbitol. Plant-based systems may use starches, carrageenan or other polymer combinations, but their processing windows can differ considerably from conventional gelatin.
Typical softgel applications
- Fish oil and omega-3 products
- Fat-soluble vitamins
- Botanical oils and lipid-based formulations
- Pharmaceutical solutions and suspensions
- Cosmetic serums and unit-dose formulations
- Veterinary oils and liquid products
Softgels can mask unpleasant tastes and odors, provide a hermetically sealed unit and create distinctive oval, oblong, round, tube or special shapes. However, not every liquid is compatible with a softgel shell. Water activity, solvent properties, pH, fill migration and shell-fill interactions must be evaluated during development.
Unlike a hard capsule filling line, a softgel plant must prepare the shell mass and fill material, encapsulate the product, perform primary tumble drying and complete final drying under controlled environmental conditions. Read the detailed softgel manufacturing process for the full production sequence.
Advantages of softgels
- Well suited to many oil-based and liquid formulations
- One-piece sealed format
- Consumer-friendly surface and shape
- Taste and odor masking
- Potential formulation benefits for certain poorly water-soluble active ingredients
- Strong visual differentiation for supplement and cosmetic products
Limitations of softgels
- More complex manufacturing and environmental control
- Mandatory drying process for conventional rotary-die softgels
- Fill and shell compatibility restrictions
- Higher formulation-development and tooling requirements
- Cleaning and process control across multiple connected systems
For a simpler overview of this dosage form, see what soft capsules are.
3. Liquid-Filled Hard Capsules
Best suited to selected non-aqueous liquids, lipid systems and semi-solids
Liquid-filled hard capsules occupy the space between dry-filled hard capsules and softgels. They use prefabricated two-piece shells, but the contents are liquid or semi-solid. After dosing, the cap and body require a validated seal—commonly banding or another closure technology—to reduce leakage risk and provide appropriate integrity.
This format can reduce some of the shell-preparation and drying complexity associated with softgel production. It may also support smaller development batches and faster changeover. However, shell compatibility remains essential. A formulation containing too much available water, a shell-reactive solvent or a volatile component may cause softening, brittleness, deformation or leakage.
Manufacturers considering omega-3 and similar products can review the more detailed comparison of liquid-filled hard capsules versus softgels.
Types of Capsules by Shell Material
Gelatin capsules
Gelatin is produced through the controlled processing of animal collagen. Depending on the supply chain and specification, sources may include bovine, porcine, fish or other approved materials. Gelatin is widely used because of its film-forming behavior, mechanical properties and established manufacturing history.
Gelatin can be used in both hard capsules and plasticized softgel shells. The formulations are not identical: a hard shell is designed to remain rigid, while a softgel shell includes plasticizer to remain flexible. Learn more about what gelatin capsules are made of.
Consider gelatin when: established performance, broad availability and conventional filling processes are priorities. Confirm animal origin, religious or dietary requirements, storage conditions and potential cross-linking risks for the specific formulation.
HPMC capsules
Hydroxypropyl methylcellulose, also called hypromellose or HPMC, is a cellulose-derived polymer used widely for two-piece vegetarian capsules. It is frequently selected for products marketed to vegetarian consumers and for formulations that benefit from a lower-moisture shell environment.
HPMC capsules are not automatically superior to gelatin capsules. Shell dimensions, electrostatic behavior, brittleness, locking characteristics and compatibility with the filling machine must be tested. The best material depends on the formulation, storage environment, label requirements and processing conditions. See the detailed guide to HPMC capsule ingredients, uses and benefits.
Consider HPMC when: a non-animal shell, low-moisture environment or specific stability profile is required. When switching from gelatin, perform machine trials rather than assuming identical settings.
Pullulan capsules
Pullulan is a polysaccharide produced by microbial fermentation. It can form clear films and is used for selected vegetarian capsule products. Pullulan capsules are often considered where oxygen-barrier performance, clean-label positioning or plant-based sourcing is important.
Availability, price, dimensional behavior and product-specific compatibility should be compared with HPMC and gelatin. “Vegetarian capsule” is a market category, not a complete engineering specification; the actual polymer and manufacturing system must be named.
Starch-based and other plant-based shells
Starch, carrageenan and blended polymer systems are used in certain hard or soft capsule technologies. These materials may support animal-free product claims, but they do not all behave alike. Melting, holding, ribbon formation, sealing, drying and storage conditions may differ by system.
For softgels in particular, the supplier should demonstrate the intended shell formulation with the actual machine, tooling and fill material. A general statement that a machine is “veggie compatible” is not enough for production qualification.
| Shell Material | Typical Capsule Format | Main Reasons to Select It | Points to Verify |
|---|---|---|---|
| Gelatin | Hard capsules and softgels | Established processing, availability, film properties | Animal origin, moisture, cross-linking, dietary requirements |
| HPMC | Mainly hard two-piece capsules | Vegetarian positioning, lower shell moisture | Static, dimensions, machine setup, sealing method |
| Pullulan | Hard two-piece capsules | Fermentation-derived material, clear film, oxygen barrier | Supply, cost, dimensions and formulation compatibility |
| Starch/polymer blends | Selected hard capsules and plant-based softgels | Animal-free shell systems and specialized applications | Supplier-specific processing, sealing and drying window |
For a direct material decision, use the complete gelatin versus HPMC capsule comparison.
Types of Capsules by Filling Material
Powder-filled capsules
Powder is the most common hard-capsule fill. Successful dosing depends on bulk and tapped density, flowability, particle-size distribution, compressibility, cohesion, moisture sensitivity and lubrication. Automatic equipment commonly forms a measured powder plug or slug before transferring it into the capsule body.
A formulation that performs well during manual filling may behave differently at commercial speed. Before scale-up, evaluate weight variation, slug strength, powder loss, dust extraction and the cleaning burden. See how to fill powder into hard capsules for a step-by-step technical guide.
Granule-filled capsules
Granulation can improve flow, reduce segregation or modify dissolution behavior. Granules may be filled volumetrically or through equipment configured for their size and flow characteristics. Fragile granules require gentle handling to avoid excessive attrition.
Pellet- and bead-filled capsules
Pellets allow multiple components or release profiles within one capsule. Different pellet populations can be combined, provided the dosing system controls each fraction accurately. Coated pellets should not be crushed or abraded during filling because damage may change their release behavior.
Commercial production may require a dedicated pellet capsule filling machine or an optional pellet-dosing station on a compatible platform.
Mini-tablets and combination fills
A hard capsule can contain one or more mini-tablets, pellets, powder or combinations of these components. This provides formulation flexibility, but every component requires controlled feeding, counting or dosing. The equipment proposal must specify which combinations are standard, optional or unsupported.
Liquid- and semi-solid-filled capsules
Liquids may be filled into softgels or compatible hard capsules. The selection depends on viscosity, temperature, water activity, solvent system, required seal, batch size and the desired commercial presentation. Softgels typically use positive-displacement dosing into the rotary-die wedge, while liquid-filled hard capsules use a dosing unit followed by sealing or banding.
Types of Capsules by Release Profile
The shell alone does not always control drug release. In many products, the release mechanism is created by the coated pellets, matrix granules, mini-tablets or formulation inside the capsule. Product developers must distinguish the capsule’s physical structure from the drug-delivery system it contains.
Immediate-release capsules
Immediate-release capsules are intended to release their contents without a deliberately added delay or extended-release mechanism. The shell first disintegrates, after which the formulation disperses and the active ingredient dissolves according to its properties. Capsule disintegration and drug dissolution are related but not identical tests.
Delayed-release and enteric capsules
Delayed-release products postpone release until a defined condition is reached. Enteric systems are designed to resist the gastric environment and release later in the intestinal tract. This may be achieved through functional capsule shells, coating the filled capsule or filling enteric-coated pellets into a conventional shell.
Do not describe every softgel as “stomach-acid resistant.” A standard softgel is not automatically enteric. Enteric performance requires a specifically designed and validated system.
Extended- and controlled-release capsules
Extended-release capsules release active ingredients over a longer period than an immediate-release product. Controlled-release is often used for systems designed to follow a more defined release pattern. In hard capsules, this behavior may come from coated beads, pellets, matrices or mini-tablets.
The filling machine must preserve the integrity and ratio of these components. Release performance is then demonstrated through appropriate dissolution testing; it cannot be inferred only from the capsule’s appearance.
Multiparticulate and pulsatile systems
Multiparticulate capsules contain multiple discrete units such as pellets or mini-tablets. Different populations may release at different times or locations. Pulsatile systems are engineered to produce one or more delayed release events. These products offer development flexibility but require accurate multi-component dosing and careful prevention of segregation.
Hard Capsule Sizes: 000 to 5
Standard hard capsules are commonly identified from size 000, the largest widely used human format, down to size 5, one of the smallest. A larger number means a smaller capsule. Capacity is a volume, not a fixed fill weight: the mass that fits inside depends on the powder’s density and how the process compacts it.
| Capsule Size | Approximate Nominal Volume | Typical Selection Consideration |
|---|---|---|
| 000 | About 1.37 mL | Very high fill volume; swallowing and machine format must be considered |
| 00 | About 0.91 mL | High-dose supplements and low-density powders |
| 0 | About 0.68 mL | Common balance between capacity and swallowability |
| 1 | About 0.50 mL | Moderate fills and smaller finished dosage form |
| 2 | About 0.37 mL | Lower-dose products or denser formulations |
| 3 | About 0.30 mL | Small doses and compact presentation |
| 4 | About 0.21 mL | Low-volume fills; handling precision becomes more demanding |
| 5 | About 0.13 mL | Very small doses and specialized applications |
Values are approximate because dimensions and usable internal volume can vary by capsule design and supplier. Final selection should use physical trials with the actual shell and formulation. For detailed dimensions and weight examples, use the complete industrial capsule size chart. For formulation calculations and machine setup, see the capsule size selection guide.
Hard Capsules vs Softgels
| Comparison | Hard Capsule | Softgel |
|---|---|---|
| Structure | Rigid two-piece cap and body | Flexible one-piece sealed shell |
| When shell is made | Before filling, normally by a separate shell manufacturer | During encapsulation at the product manufacturer’s plant |
| Typical fills | Powder, granules, pellets, beads and mini-tablets | Oils, solutions, suspensions and suitable semi-solids |
| Liquid filling | Possible with compatible non-aqueous fills and validated sealing | A primary application of the format |
| Main machine | Hard capsule filling machine | Rotary-die softgel encapsulation machine |
| Drying after filling | Normally no shell-drying stage for prefabricated hard capsules | Primary and final drying are normally required |
| Changeover | Change parts and dosing setup vary by capsule size and fill system | Die rolls, wedge, pump setup and process conditions vary by product |
| Typical project complexity | Low to high, depending on dosing and containment | Higher because preparation, encapsulation, drying and environment are connected |
Neither type is universally better. Hard capsules are usually the first option for powders and multiparticulates. Softgels are often selected for oils and compatible liquid systems. Liquid-filled hard capsules can be a valuable third route where a two-piece shell and sealed liquid dose meet the product requirements.
For a broader dosage-form comparison, read tablets versus capsules.
Which Equipment Is Required for Each Capsule Type?
Equipment for powder-filled hard capsules
A commercial line may include material preparation or granulation, powder handling, an automatic capsule filling machine, capsule polishing, metal detection, inspection and packaging. The filler separates empty capsules, doses the product, closes the shells and rejects incomplete units.
The machine configuration must match the product. Powder dosing, pellet dosing, tablet insertion, liquid dosing and containment are not interchangeable assumptions. Buyers should define every fill component in the user requirement specification.
Equipment for liquid-filled hard capsules
The line normally requires liquid preparation and temperature control, precision dosing, capsule filling, sealing or banding, leak inspection and curing or handling according to the sealing system. The shell supplier and equipment manufacturer should jointly confirm compatibility.
Equipment for softgel capsules
A complete softgel line can include gelatin or shell-mass preparation, fill-material mixing and homogenization, service tanks, a softgel encapsulation machine, chillers, tumble dryers, final drying, sorting, inspection and cleaning equipment. Capacity must be balanced across the whole line.
The encapsulator’s maximum output is not the factory output if preparation or drying cannot keep pace. Shell formulation, capsule size, fill viscosity, die design, room conditions and reject rate all influence saleable production.
Equipment for modified-release capsules
If release behavior comes from coated pellets or granules, the project may require fluid-bed coating or other particle-processing equipment before filling. If the filled capsule itself is coated, a suitable coating process follows filling and closing. The filling machine must handle the components without damaging functional coatings.
How to Select the Right Type of Capsule
Step 1: Define the fill material
Identify whether the product is a powder, granule, pellet, mini-tablet, oil, solution, suspension or semi-solid. Measure relevant properties such as density, flowability, viscosity, particle size, water activity and temperature sensitivity.
Step 2: Define the required release profile
Decide whether the product is immediate release, delayed/enteric, extended release or multiparticulate. Determine whether the release mechanism belongs in the shell, coating or internal formulation.
Step 3: Screen shell compatibility
Compare gelatin, HPMC, pullulan or a specialized plant-based system based on formulation stability, water sensitivity, oxygen exposure, dietary claims, regulatory status and machine behavior. Do not select a shell solely from marketing language.
Step 4: Select size and geometry
For hard capsules, calculate the required volume from the validated formulation density and confirm it by trial. For softgels, define dose, fill density, shape, dimensions and target output before designing the die roll.
Step 5: Match the manufacturing platform
Choose a hard-capsule filler, liquid-filled hard-capsule line or softgel system based on the formulation and production route. Review cleaning, changeover, containment, tooling, utilities, documentation and downstream inspection.
Step 6: Run formulation-specific trials
Use the actual shell and representative fill material. Measure fill-weight variation, capsule integrity, leakage, rejects, stability and line output. For modified-release products, confirm that manufacturing does not damage the release-control system.
Simple decision rule:
- Start with a hard capsule for most powders, granules, pellets and mini-tablets.
- Compare a softgel with a liquid-filled hard capsule for suitable oils, liquids and semi-solids.
- Use a functional shell, coating or multiparticulate system when delayed or extended release is required.
- Validate the complete formulation-shell-machine combination before commercial purchase.
Common Capsule Selection Mistakes
Treating every vegetarian capsule as the same
HPMC, pullulan and plant-based softgel systems have different compositions and processing behavior. Specify the actual material and supplier.
Assuming capsule size equals fill weight
Capsule size defines approximate volume. Fill weight changes with density and compaction. Physical trials are required.
Calling every delayed-release product enteric
Enteric release is a specific form of delayed release associated with resistance to gastric conditions. The performance must be demonstrated using the appropriate test.
Assuming a standard softgel resists stomach acid
A conventional softgel is not automatically enteric. An enteric product requires a functional shell, coating or other validated design.
Selecting the machine before the dosage form
The formulation and capsule architecture determine the production route. Buying equipment before confirming them may lock the project into an unsuitable process.
Ignoring the downstream process
Softgel drying, hard-capsule sealing, inspection and packaging can limit output or affect product quality. Evaluate the complete line rather than the main filler alone.
Frequently Asked Questions
What are the two main types of capsules?
The two main structural types are hard two-piece capsules and soft one-piece capsules, usually called softgels. Liquid-filled hard capsules are a specialized application of the two-piece hard-capsule format.
What are pharmaceutical capsules made of?
Common shell materials include gelatin and HPMC. Pullulan and specialized starch or polymer systems are also used. Softgel shells normally contain a film-forming polymer, water, plasticizer and any approved color or opacity components required by the product.
What is the difference between gelatin and vegetarian capsules?
Gelatin is derived from processed animal collagen. Vegetarian shells may use HPMC, pullulan or other non-animal polymer systems. Their moisture, oxygen-barrier, mechanical and machine-handling properties differ, so selection should be product-specific.
Which capsule type is best for powder?
A two-piece hard capsule is normally the first option for powder. Final suitability depends on powder density, flow, compressibility, dose and stability.
Which capsule type is best for oil?
Softgels are widely used for oils. Liquid-filled hard capsules may also be suitable when the oil is compatible with the shell and the closed capsule receives a validated seal.
Can hard capsules contain liquid?
Yes, selected non-aqueous liquids and semi-solids can be filled into compatible hard capsules. The cap-body joint normally requires a validated sealing or banding process.
Can softgels contain powder?
Softgels are not normally filled with loose dry powder. Insoluble particles may be dispersed in a compatible liquid vehicle to create a suspension, but particle size, sedimentation, viscosity and shell compatibility must be controlled.
Are all softgels made from gelatin?
No. Gelatin remains common, but validated plant-based softgel systems are available. These alternatives may require different preparation, encapsulation and drying conditions.
What is an enteric capsule?
An enteric capsule is designed to resist release in the gastric environment and release later under intestinal conditions. The function may come from the shell, an applied coating or enteric-coated contents.
Do capsules dissolve faster than tablets?
There is no universal answer. Shell disintegration, formulation dissolution, tablet coating, excipients and test conditions all affect performance. See the guide to how long capsules take to dissolve.
What is the largest standard capsule size?
Size 000 is commonly the largest standard two-piece hard capsule used for human oral products, while size 5 is among the smallest. Other specialized and veterinary formats also exist.
Can one capsule filling machine handle every capsule type?
No. Hard capsules and softgels require fundamentally different machinery. Even within hard-capsule filling, powder, pellet, tablet and liquid dosing may require different stations or optional systems.
How do I choose between a hard capsule and a softgel?
Start with the fill material and production route. Hard capsules generally suit powders and multiparticulates. Softgels suit many oils and compatible liquid or semi-solid formulations. Compare stability, release goal, batch size, consumer requirements and equipment investment before deciding.
Conclusion
The main capsule structures are hard two-piece capsules and softgels, but a useful selection goes further. Shell material, fill type, release behavior, size and manufacturing equipment must all work as one system.
For dry powders and multiparticulates, hard capsules normally offer the most direct route. For oils and suitable liquids, compare softgel technology with liquid-filled hard capsules. When delayed or extended release is required, determine whether the control mechanism belongs in the capsule shell, the coating or the contents.
The final choice should be supported by compatibility studies, production trials and a clearly defined equipment specification—not by capsule appearance or a single marketing claim.
Need Help Matching a Capsule Type to Production Equipment?
Send URMACHINE your capsule material, size, formulation properties, target fill weight, release requirement and hourly output. The technical team can recommend a suitable hard-capsule filling, liquid-capsule or softgel production configuration.
Compare automatic capsule filling machines or review softgel encapsulation equipment.
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