What Are Capsules Made Of? Medicine Capsule Materials

A practical guide to capsule shell materials, fill ingredients, manufacturing compatibility, and quality control

Medicine capsules have two separate material systems: the shell and the fill. The shell is commonly made from gelatin, hypromellose or HPMC, pullulan, or a specialized starch and polymer blend. Hard capsules use a rigid two-piece cap and body. Traditional softgels use a flexible mixture of gelatin, water, and a plasticizer such as glycerol or sorbitol, although non-gelatin soft capsule technologies also exist.

Inside the shell, the fill contains the active pharmaceutical ingredient and any excipients needed for dose uniformity, flow, stability, disintegration, or release. Depending on the product, the fill may be a powder, granule, pellet, mini-tablet, non-aqueous liquid, suspension, paste, or semisolid. Colors, opacifiers, printing inks, gelling aids, and preservatives may also be present, but their use is product-specific.

The short answer is therefore not simply gelatin. A manufacturer must identify the exact shell polymer, every shell additive, the fill formulation, the dosage-form structure, and the intended release profile before selecting a capsule and filling process.

Key Takeaways:

• Most hard medicine capsules use gelatin or HPMC, while pullulan and specialized polymer blends serve selected applications.
• Traditional softgels usually combine gelatin, water, and a plasticizer around a compatible liquid or semisolid fill.
• The capsule shell is not the medicine inside it: the fill contains the active ingredient and product-specific excipients.
• Ordinary HPMC capsules are not automatically enteric or delayed release; those functions require a validated capsule or coated-particle system.
• A capsule should be opened, mixed, or divided only when the medicine label or a qualified healthcare professional confirms that method is appropriate.

Capsule Shell and Fill at a Glance

The Capsule Shell Is Not the Medicine Inside

A capsule is a dosage form, not one raw material. The shell acts as a container that carries the formulated dose through manufacturing, packaging, storage, and administration. The fill provides the drug or supplement and the excipients that help deliver it consistently.

This distinction matters when reading a label or discussing compatibility. A product may have a gelatin shell while its powder fill contains microcrystalline cellulose, lactose, starch, silica, magnesium stearate, or other excipients. Another product may use an HPMC shell around coated pellets. A softgel may use a plasticized gelatin shell around an oil solution. Each combination creates different moisture, oxygen, mechanical, and release risks.

It is also useful to separate capsules from caplets. A caplet is a capsule-shaped compressed tablet. It does not have a cap and body, and its composition and manufacturing process follow tablet technology rather than capsule-shell technology.

Hard and Soft Capsules Use Different Structures

Hard Two Piece Capsules

A hard capsule consists of a longer body and a shorter cap. Empty shells are made first, supplied to the medicine manufacturer, separated during filling, and then closed or locked after the formulation enters the body. Powders, granules, pellets, mini-tablets, and combinations of these are common fills. Selected hard capsules can also hold compatible non-aqueous liquids or semisolids when an appropriate sealing process is used.

The word hard describes the shell structure, not the source material. Many hard capsules use gelatin, but HPMC and pullulan hard shells are commercially available. Their polymer, gelling system, water level, dimensions, surface properties, and locking design can affect how they run on a filling machine.

Softgel Capsules

A softgel is normally formed, filled, and sealed in one continuous operation. Two shell ribbons pass through rotating dies while a dosing system delivers the liquid or semisolid fill between them. Heat and pressure create the seam and cut the individual capsules. The wet capsules then require controlled drying.

Traditional softgel shells contain gelatin, water, and a plasticizer. The plasticizer keeps the dried shell flexible. Glycerol and sorbitol are common examples, but the actual blend depends on the fill, climate, desired texture, and manufacturing process. Plant-based soft capsule systems may use starches, carrageenan, or other polymer combinations and require supplier-specific preparation and drying conditions.

Gelatin Capsule Shells

Where Gelatin Comes From

Gelatin is produced by controlled hydrolysis of collagen from qualified animal tissues. Commercial pharmaceutical gelatin may come from bovine, porcine, fish, or another approved source. The exact origin is a supply-chain and labeling fact that should be confirmed through the material specification and supplier documentation.

Gelatin forms strong, clear films and undergoes reversible gelation that supports the pin-dipping process used to make hard capsule shells. It also works well with plasticizers in flexible softgel films. Its long manufacturing history and broad equipment compatibility explain its continued use in pharmaceutical and nutraceutical products.

What Is Added to Gelatin Shells

Water is essential during shell formation and remains at a controlled level in the finished shell. Hard gelatin capsules usually rely on the relationship between gelatin and water to maintain flexibility. If the shell loses too much water, it can become brittle. If it absorbs excessive moisture, it can soften, distort, or stick.

Product-specific shells may also contain approved colors, opacifiers, processing aids, preservatives, or printing inks. A clear capsule can have a simpler visible composition than an opaque printed capsule, but the actual formula must come from the supplier or approved product record. Color alone cannot identify the polymer or prove that a shell is suitable for a particular market.

Gelatin Compatibility Risks

Gelatin contains reactive amino groups. Certain aldehydes or degradation products can promote cross-linking, which creates a less soluble film or pellicle. The effect may appear during storage and can change disintegration or dissolution behavior. Formulators should investigate the fill, packaging, temperature, humidity, and aging conditions rather than treating a dissolution change as a machine problem.

Animal origin also creates sourcing requirements. Bovine, porcine, and fish gelatin are not interchangeable claims. Supplier qualification may need species and tissue origin, traceability, microbiological controls, transmissible spongiform encephalopathy documentation where applicable, and certificates supporting halal, kosher, or other market requirements.

HPMC Capsule Shells

What HPMC Means

HPMC is the common abbreviation for hydroxypropyl methylcellulose, also called hypromellose. It is a cellulose-derived, non-animal polymer used widely for hard two-piece capsules. Calling it a vegetable capsule is convenient for consumers, but HPMC is a chemically modified cellulose ether rather than an unprocessed plant material.

Commercial HPMC shells do not all use the same technology. Some formulations use a secondary gelling agent and salts, while other systems use thermogelation or proprietary processes. Those differences can affect dissolution in certain media, shell dimensions, moisture behavior, and machine handling. The shell supplier and grade should therefore remain part of the controlled product definition.

Why Manufacturers Choose HPMC

HPMC shells normally contain less water than conventional hard gelatin shells. That can help formulations that are sensitive to moisture transfer, although it does not guarantee stability. HPMC also avoids an animal-derived shell and may support vegetarian or vegan positioning when every component and process meets the relevant claim.

The material is less susceptible to gelatin-type cross-linking. It can still interact with the fill, environment, package, and dissolution medium. Product development should compare real stability and release data rather than selecting HPMC from a general list of advantages.

HPMC Filling Considerations

Switching from gelatin to HPMC may change feeding, orientation, cap-body separation, closing, static behavior, and defect rates. Small dimensional or surface-friction differences can matter at production speed. A shell that works in a manual bench test may not separate reliably on an automatic machine.

Use the intended supplier, size, color, print, and lot during trials. The HPMC capsule filling guide explains how to evaluate storage, vacuum separation, closing length, shell damage, and speed. Do not copy settings from gelatin production without confirming the result.

Pullulan and Other Non Gelatin Shells

Pullulan Capsules

Pullulan is a polysaccharide produced by microbial fermentation. It can form clear films and is used in selected hard capsule systems. Manufacturers may consider it for non-animal positioning and for formulations that benefit from its barrier profile. The commercial shell may also contain a gelling aid or other ingredients, so the polymer name does not describe the complete formula.

Pullulan performance should be evaluated with the actual fill and package. Supply availability, cost, shell dimensions, moisture transfer, oxygen transmission, storage, disintegration, and machine behavior can differ from HPMC or gelatin. Broad claims such as natural or oxygen protective require evidence and market-appropriate wording.

Starch and Polymer Blend Capsules

Starch, carrageenan, gellan gum, alginate, and other polymers may appear in specialized hard or soft capsule systems. Some act as the main film former, while others support gelation or mechanical strength in a blend. A label such as plant based does not reveal which role each ingredient performs.

These systems are technology-specific. Their solution preparation, dipping or ribbon formation, drying, sealing, and storage windows may differ substantially. Manufacturers should obtain the complete composition allowed by confidentiality arrangements, a regulatory support package, and process data for the proposed application.

Capsule Shell Additives

Water and Plasticizers

Water supports polymer processing and affects the mechanical state of the finished shell. In hard gelatin capsules, too little retained moisture can increase brittleness. In softgels, water leaves progressively during drying while the polymer and plasticizer establish the final structure.

Plasticizers reduce intermolecular forces and help a soft shell remain flexible. Glycerol and sorbitol are widely used, but their ratio can influence hardness, drying, water activity, and interaction with the fill. A hydrophilic fill can draw plasticizer or water across the shell, while a volatile or migrating component can weaken the seam or change texture.

Colors Opacifiers and Printing Inks

Capsule shells may be clear, naturally colored, pigmented, or opaque. Color can help identify strengths and reduce medication-selection errors, while an opacifier may protect a light-sensitive fill. Printed codes can support identification and brand control.

Every color and ink component must be suitable for the intended use and market. Requirements can differ among countries, medicines, and supplements. Manufacturers should control the approved formula, supplier, print specification, migration risk, legibility, and change history. A visually similar replacement is not automatically a regulatory equivalent.

Gelling Aids and Processing Ingredients

Some non-gelatin shells use carrageenan, gellan gum, or salts to establish a gel during manufacturing. Surfactants, preservatives, or other processing ingredients may also be present in specific systems. Their necessity and level depend on the polymer, process, and supplier.

These ingredients can influence shell formation and behavior in disintegration or dissolution media. Ask for a complete qualitative composition, compendial status where relevant, residual limits, and evidence that the shell remains suitable throughout shelf life.

What Goes Inside a Medicine Capsule

Active Pharmaceutical Ingredient

The active pharmaceutical ingredient provides the intended pharmacological action. A capsule may contain one active or several. The active can be present as a crystalline or amorphous powder, granules, coated pellets, mini-tablets, a solution, a suspension, or another engineered form.

Dose alone does not determine capsule size. Bulk density, tapped density, particle size, flow, compressibility, and the required excipients determine how much formulated material fits into the available volume. Two formulations with the same milligram dose can require different capsule sizes.

Powder Fill Excipients

Powder formulations often use diluents to build volume, glidants to improve flow, lubricants to reduce friction, and disintegrants to help the plug or powder mass disperse. Surfactants, pH modifiers, antioxidants, adsorbents, or stabilizers may be added when justified by the product design.

An excipient is not automatically inactive from a manufacturing perspective. A small change in lubricant level can alter powder movement, plug strength, ejection, wetting, and dissolution. The capsule excipient guide connects common excipient functions with dosing behavior and fill-weight variation.

Pellets Granules and Mini Tablets

Multiparticulate fills allow formulators to combine units with different coatings or release profiles in one capsule. A capsule may contain immediate-release granules and delayed-release pellets, or several mini-tablets with separate functions. The outer shell is then only one part of the release system.

Particle size distribution, electrostatics, segregation, counting accuracy, coating damage, and available fill volume require control. Equipment trials should confirm that the dosing mechanism does not abrade functional coatings or separate a mixture during feeding.

Liquid and Semisolid Fills

Softgels commonly contain oils, non-aqueous solutions, suspensions, or pastes. Selected hard capsules can also hold compatible liquids or molten semisolids followed by banding or another seal. The fill must not dissolve, swell, embrittle, or excessively plasticize the shell.

Water activity, solvent migration, viscosity, suspended-particle settling, oxidation, seam integrity, and leakage all affect stability. A fill that appears compatible immediately after encapsulation can change during accelerated or long-term storage, so package selection and stability testing are part of the formulation decision.

Material Comparison for Manufacturers

No material is best for every product. The right choice is the shell that meets the formulation, release, label, market, process, package, and shelf-life requirements with reproducible evidence.

How Hard Capsule Shells Are Manufactured

Hard capsule production commonly uses polished metal pins shaped like the cap and body. The process includes dipping the pins into a controlled polymer solution, rotating or spinning them to distribute the film, drying the shells, stripping them from the pins, trimming them to length, and joining the cap and body.

Gelatin and non-gelatin systems may need different solution temperatures, gelation mechanisms, drying conditions, and environmental controls. The finished shells are inspected for dimensions, wall consistency, visual defects, moisture, locking performance, and other specification requirements before packing.

During medicine production, an automatic capsule filling machine or semi-automatic system separates these prefabricated shells, doses the fill, closes the cap and body, and ejects the finished capsule. Capsule-shell manufacturing and capsule filling are related but separate operations.

How Softgel Shells Are Manufactured

Softgel manufacture prepares a molten or flowable shell mass and a compatible fill formulation. The encapsulation machine casts two ribbons, meters the fill, forms matched pockets in rotary dies, seals the ribbons around the dose, and cuts each capsule. The seam forms while the shell is warm and plastic.

Fresh softgels contain more water than the final product. Tumble drying and controlled room drying remove water until the shell reaches its target mechanical and stability state. Drying too quickly can create case hardening or distortion, while insufficient drying can leave soft, sticky capsules.

The softgel manufacturing process guide covers gelatin preparation, fill preparation, ribbon formation, encapsulation, drying, inspection, and packaging in more detail.

How Shell Material Affects Filling Equipment

Feeding and Separation

Hard capsules must orient consistently and enter the correct segment pockets. Vacuum and mechanical alignment then separate the cap from the body. Dimensional variation, static, deformation, joined-capsule condition, storage humidity, and surface friction can increase non-separation or misfeed rates.

Trial records should distinguish shell-related defects from machine setup and fill-related contamination. Document capsule supplier, lot, size, color, print, storage exposure, vacuum, speed, and rejected-capsule categories.

Dosing and Closing

The shell determines available volume and influences closing behavior, while the fill determines the dosing mechanism and consolidation required. Tamping-pin and dosator systems meter powders differently. Pellets may need gentle handling, and liquids need pumps and sealing controls.

Closing length and force must secure the cap without telescoping, dimpling, splitting, or unlocking. Confirm the locked length with the actual shell rather than relying only on a nominal size. The automatic capsule filling machine buying guide provides a broader requirements checklist for capsule, formulation, output, utilities, and factory testing.

Packaging and Storage

The package controls the environment around the capsule after filling. Moisture-sensitive or oxygen-sensitive combinations may require a high-barrier blister, bottle liner, desiccant, oxygen absorber, or controlled headspace. The choice must be supported by stability data rather than the shell material name alone.

A blister packing machine must form pockets without damaging the shell and seal the selected barrier material consistently. Bottling lines must control drops, abrasion, count accuracy, and closure integrity. Capsules should also be evaluated after realistic transport and storage exposure.

Can You Open a Medicine Capsule?

Do not decide from the shell material alone. Some immediate-release hard capsules can be opened and their contents mixed with a small amount of suitable food or liquid, but only when the product instructions or a qualified healthcare professional confirms that method. Other capsules must remain intact to protect the dose, control release, prevent irritation, or keep the user from contacting the contents.

Do not crush or chew enteric-coated pellets, delayed-release beads, extended-release particles, hazardous drugs, or any capsule whose directions require it to be swallowed whole. Opening the outer shell does not necessarily destroy coated particles inside, but chewing or grinding those particles can defeat their release function. A product may also be unsuitable for mixing with a particular food, drink, or feeding tube.

Guidance from Medicines for Children illustrates the product-specific approach: some capsules may be opened, dispersed, or sprinkled, while the label, pharmacist, doctor, or nurse should determine whether and how this is done. Manufacturers should write administration instructions from formulation and stability evidence rather than from the general word capsule.

Quality Tests for Capsule Materials

Tests and limits depend on the dosage form, pharmacopoeial requirements, approved application, and market. Empty-shell certificates are useful incoming evidence, but finished-product testing is still necessary because filling, sealing, packaging, and storage can change performance.

How to Choose a Capsule Material

Begin with the formulation rather than a dietary claim or price comparison. Record the active ingredient, excipients, physical fill form, dose, water activity, solvent system, sensitivity to moisture and oxygen, and target release. Then compare shell systems using the same stability and manufacturing endpoints.

Use this selection sequence:

1. Define whether the product requires a hard two-piece capsule or a soft one-piece capsule.
2. Identify all shell and fill components that must meet regulatory, dietary, religious, or allergen-related requirements.
3. Screen shell-fill interactions using moisture, migration, cross-linking, leakage, and release studies.
4. Confirm that the dose fits the capsule volume at a practical bulk density and dosing setting.
5. Run the intended capsule supplier and grade on the planned filling and sealing equipment.
6. Select packaging from stability evidence for the complete shell-fill system.
7. Lock the supplier, composition, dimensions, printing, storage, test methods, and change-control requirements into the specification.

The decision should remain product-specific. A lower-moisture shell can still absorb water in a humid room. An oxygen-barrier claim cannot compensate for a permeable package or oxygen-rich headspace. A capsule that fills cleanly can still fail dissolution after storage.

Common Capsule Material Problems

Brittle Hard Capsules

Brittleness can follow moisture loss, unsuitable storage, excessive drying, cold handling, or a shell-fill moisture imbalance. Review environmental history and shell moisture before increasing machine force or changing tooling. Mechanical adjustments cannot restore a damaged shell lot.

Soft or Sticky Capsules

Excess humidity, incomplete drying, a migrating fill component, or unsuitable packaging can soften the shell. Check water activity, plasticizer and solvent movement, drying endpoint, storage, and package barrier. Surface treatment should not hide an unresolved compatibility problem.

Cross Linked Gelatin

Gelatin cross-linking may create a membrane that resists normal dissolution. Potential contributors include aldehydes, peroxide-related degradation products, heat, humidity, and time. Investigation may require chemical analysis, dissolution testing with justified enzyme conditions, and comparison of aged and control samples.

Capsules That Fail to Separate

Non-separation can result from distorted shells, dimensional variation, high or low humidity, static, contamination, incorrect vacuum, worn segments, or poor alignment. Separate incoming-shell inspection from equipment checks and evaluate defects by capsule lot and machine station.

Leakage or Weak Softgel Seams

Seam failures can come from ribbon thickness variation, temperature, die alignment, fill contamination at the seam, inadequate pressure, or shell-fill incompatibility. Inspect seam geometry and leakage patterns before changing several process variables at once.

Frequently Asked Questions

References

The Shell Dissolution of Various Empty Hard Capsules, comparison of gelatin, gelatin with PEG, and HPMC shell dissolution under different conditions.
The Effect of Cross Linking on Hard Gelatin Capsule Disintegration, clinical investigation of stressed gelatin capsules.
Are Your Capsules Vegetarian or Nonvegetarian, review of gelatin and non-gelatin capsule materials.
Preparation Properties and Potential of Carrageenan Based Hard Capsules, review of alternative capsule materials and hard-shell manufacturing steps.
Industrial Manufacture of Enteric Hard Capsules, discussion of hard-capsule materials and functional shell development.
USP Disintegration Harmonization Text, compendial disintegration concepts for capsules and tablets.
FDA Dosage Forms, official distinctions among capsules, coated capsules, delayed-release capsules, and delayed-release pellets.
How to Give Medicines: Capsules, product-specific safety guidance on swallowing, opening, mixing, dissolving, and sprinkling capsule contents.