Most supplement capsules are made from one of two materials: gelatin (an animal protein) or HPMC (a plant-derived cellulose). The one you’re holding depends on the brand’s cost targets, the dietary preferences of its customers, and what’s inside the capsule. Beyond those two main shell materials, capsules contain small amounts of plasticizers, colorants, and sometimes coatings that control where in your digestive tract the contents are released.
Gelatin: The Traditional Standard
Gelatin capsules have been the default in the supplement industry for over a century. Gelatin is a protein made by breaking down collagen from animal skin, bones, and connective tissue, typically sourced from cows, pigs, or fish. The raw collagen goes through a multi-step process of cleaning, chemical pretreatment, extraction, filtration, sterilization, and drying before it becomes the clear, dissolvable shell you swallow.
Two main types exist based on how the collagen is processed. Type-A gelatin uses an acid treatment, which is the more common method. Type-B gelatin uses an alkaline treatment. Both are classified as Generally Recognized As Safe (GRAS) by regulators and approved for pharmaceutical use by the U.S. Pharmacopeia and European Pharmacopeia. The source animal matters if you follow halal, kosher, or vegetarian dietary rules. Most labels specify “bovine gelatin” or “porcine gelatin,” though many don’t. Fish-derived gelatin is less common but growing as a halal-friendly option.
HPMC: The Plant-Based Alternative
Capsules labeled “vegetarian” or “vegan” are almost always made from hydroxypropyl methylcellulose, listed on labels as HPMC or sometimes “vegetable cellulose.” It’s a semi-synthetic material derived from natural cellulose, the structural fiber in all plants. Manufacturers treat cellulose with chemicals that modify its structure, giving it the film-forming properties needed to shape a capsule shell.
HPMC capsules have a practical advantage beyond dietary preference. They contain less moisture than gelatin shells and don’t undergo a degradation process called cross-linking, where gelatin molecules bond together over time and make the capsule harder to dissolve. This makes HPMC a better choice for ingredients that are moisture-sensitive or chemically incompatible with gelatin. If you’ve noticed that certain probiotics, herbal extracts, or iron supplements come in opaque white capsules rather than the classic transparent gelatin look, moisture protection is often the reason.
Pullulan: A Newer Option
Some premium supplement brands use pullulan capsules, which you’ll see marketed as “fermented tapioca” or “natural plant capsules.” Pullulan is a polysaccharide (a chain of glucose molecules) produced by fermenting starch with a specific fungus. The resulting material forms clear, glossy films with an excellent oxygen barrier, meaning it protects the contents from oxidation better than standard HPMC or gelatin. This makes pullulan capsules popular for supplements containing omega-3 fatty acids, CoQ10, or other ingredients that degrade when exposed to air. They’re also vegan, non-GMO, and free of common allergens, which adds to their marketing appeal.
Hard Shells vs. Softgels
Hard capsules are the two-piece shells you can pull apart. They hold dry powders, pellets, or granules. Both gelatin and HPMC are used for hard capsules, and the shell itself is relatively simple: mostly the base material plus water, with small amounts of colorant or opacifier added.
Softgels are the one-piece, sealed capsules that hold liquids or oil-based fills. They require plasticizers to make the shell flexible enough to form and to stay pliable on the shelf. The two most common plasticizers are glycerol and sorbitol, both sugar alcohols. Research on capsule formulation shows that a blend of these two plasticizers at roughly equal ratios produces the best balance of flexibility and structural integrity. Without plasticizers, the capsule shell would be hard and brittle. Softgels are traditionally made from gelatin because it naturally forms strong, elastic films, though pullulan-based softgels are now available for vegan consumers.
Colorants and Opacifiers
The color of a capsule shell comes from added pigments. Common options include iron oxides (for browns, reds, and yellows), FD&C dyes (the synthetic colorants used in food), and natural colorants like chlorophyll or caramel. Some capsules are left clear or translucent, but many are made opaque to protect light-sensitive ingredients inside.
The most effective opacifier is titanium dioxide, a white mineral pigment listed as E171 in Europe. It’s been the subject of regulatory scrutiny. The EU banned titanium dioxide as a food additive in 2022 but temporarily kept it approved for use in medicines and supplements to avoid product shortages. A review of that decision was scheduled for 2025. In North America, titanium dioxide remains approved. The FDA reviewed the European food safety authority’s concerns and maintained that titanium dioxide is acceptable in food at concentrations up to 1% by weight. Health Canada and food regulators in Australia and New Zealand reached similar conclusions, finding no evidence that dietary exposure to food-grade titanium dioxide poses a health concern. Still, many supplement brands have moved to titanium dioxide-free capsules in response to consumer demand, though testing shows that alternatives don’t match its opacity as effectively.
Delayed-Release Coatings
Some supplement capsules are designed to survive your stomach acid and only dissolve in the intestine. These are called enteric-coated or delayed-release capsules, and they use an additional outer layer made from acid-resistant polymers. Shellac, a natural resin secreted by lac insects, is one of the oldest enteric coating materials. It resists the low pH of stomach acid (around pH 2) because its acidic chemical groups don’t easily break apart in that environment.
Synthetic options include cellulose acetate phthalate, which dissolves at a pH above 6 (matching the intestinal environment), and acrylic-based polymers that dissolve at pH 5.5 or higher. You’ll encounter delayed-release capsules most often with probiotics, digestive enzymes, and supplements that can irritate the stomach lining, like high-dose fish oil or certain herbal extracts. The coating doesn’t change the capsule’s base material. It’s simply an extra layer applied to a standard gelatin or HPMC shell.
How to Tell What Your Capsule Is Made Of
Check the “Other Ingredients” section on the supplement label. Gelatin capsules will list “gelatin” and often specify the animal source. Vegetarian capsules will say “HPMC,” “hypromellose,” or “vegetable capsule.” Pullulan capsules typically list “pullulan” directly. If you see glycerin or sorbitol alongside gelatin, you’re looking at a softgel. If the label mentions a coating material or says “delayed release,” there’s an additional polymer layer on the outside.
For most people, the capsule material makes no functional difference to how well the supplement works. The shell dissolves in your stomach within 5 to 15 minutes regardless of whether it’s gelatin or HPMC. The choice matters most if you have dietary restrictions, allergies to animal products, or you’re taking a supplement with moisture-sensitive or oxygen-sensitive ingredients where the shell material genuinely affects stability and potency over time.