Clear capsules are most commonly made of gelatin, a protein derived from animal collagen. Vegetarian alternatives made from plant-based cellulose or fermented starch are also widely available. What makes these capsules “clear” rather than opaque is simply the absence of added colorants and opacifiers like titanium dioxide, which is present in the majority of colored or white capsules on the market.
Gelatin: The Most Common Material
Gelatin is produced by breaking down collagen, the main structural protein found in animal skin, bones, and connective tissue. The three principal raw materials are cattle bones, cattle hides, and pig skins. Gelatin recovered from bone is used primarily for pharmaceutical purposes, while pig skin gelatin is more common in supplement manufacturing.
The extraction process differs depending on the animal source. Pig skins are soaked in cold dilute acid (usually hydrochloric or sulfuric acid) for several hours until they swell fully. This produces what’s called Type A gelatin. Cattle bones and hides go through a much longer treatment, soaking in an alkaline lime solution for 8 to 12 weeks. This produces Type B gelatin. In both cases, the treated material is then extracted with hot water, filtered, purified, and concentrated into the gelatin used for capsule shells.
Gelatin capsules have been used in pharmacy since the early 19th century. They come in two main forms: two-piece hard capsules (the kind you can pull apart) and soft elastic capsules, often called softgels. Hard gelatin capsule shells maintain a moisture content of 13 to 16%, which keeps them flexible enough to avoid cracking but firm enough to hold their shape.
HPMC: The Plant-Based Alternative
Capsules labeled “vegetarian” or “vegan” are typically made from hydroxypropyl methylcellulose, usually shortened to HPMC or sometimes called hypromellose. This is a semi-synthetic material derived from cellulose, the structural fiber found in all plants and wood. Natural cellulose doesn’t dissolve in water, so it’s chemically modified to make it water-soluble and suitable for capsule shells.
HPMC capsules look and function almost identically to gelatin capsules. They appeal to vegetarians, vegans, and people who avoid pork or beef products for religious reasons. They also tend to have lower moisture content than gelatin capsules, which makes them a better choice for moisture-sensitive ingredients like certain probiotics and hygroscopic powders.
Pullulan: The Fermented Option
A newer capsule material called pullulan is made through a completely different process. Rather than extracting protein from animals or modifying plant fiber, pullulan is produced by microbial fermentation. A black, yeast-like fungus called Aureobasidium pullulans feeds on a sugar substrate, typically starch syrup or tapioca, and produces pullulan as a natural byproduct. The fungus can also ferment a surprising range of agricultural sources, including beet molasses, corn steep liquor, date extract, dairy whey, and even agricultural waste products like cassava bagasse and palm kernel.
Pullulan capsules are naturally clear and dissolve easily. They’re marketed as a clean-label option because the base material comes from a straightforward fermentation process rather than chemical extraction.
What Else Goes Into a Capsule Shell
The base material alone doesn’t make a functional capsule. Several additional ingredients fine-tune the shell’s flexibility, stability, and performance.
- Plasticizers are small molecules added to prevent the capsule from becoming brittle. Glycerol and sorbitol are the two most common, especially in soft capsules. They work by loosening the tight bonds between polymer chains, creating a more flexible film. Research shows that a blend of glycerol and sorbitol together performs better than either one alone, producing capsules with the right balance of flexibility and structural strength.
- Water acts as a natural plasticizer in gelatin capsules. The 13 to 16% moisture content in hard gelatin shells is carefully controlled during manufacturing and storage.
- Gelling agents like carrageenan (from seaweed) are sometimes added to HPMC formulations to help the capsule hold its shape during production.
Opaque or colored capsules contain additional ingredients like titanium dioxide (a white pigment) and various dyes. Clear capsules skip these entirely, leaving the shell transparent or slightly translucent so you can see the contents inside.
How Clear Capsules Are Made
Most hard capsules are manufactured using a dipping method that hasn’t changed dramatically in decades. Rows of stainless steel pins, shaped like the body and cap of a capsule, are dipped into a warm liquid solution of gelatin or HPMC. The pins are then spun to distribute the coating evenly and blown with air to begin drying. Once the film has set, the dried capsule halves are stripped off the pins, trimmed to precise lengths, and joined together into the finished two-piece capsule.
Temperature, dip time, and solution concentration are tightly controlled at every step because even small variations affect the capsule’s wall thickness, dissolution rate, and structural integrity. Manufacturers adjust these parameters depending on whether they’re producing gelatin or HPMC shells, since the two materials behave differently during drying and setting.
Gelatin vs. HPMC vs. Pullulan
For most people, the choice between capsule types comes down to dietary preferences and what’s inside the capsule. Gelatin capsules are the industry standard, widely available, and inexpensive. HPMC capsules suit vegetarian or vegan diets and work better for moisture-sensitive fills. Pullulan capsules offer a fermentation-derived, plant-compatible option with a clean-label appeal.
All three dissolve readily in the stomach and release their contents within minutes. From a functional standpoint, the differences are subtle. The most practical distinction is that gelatin capsules can become sticky or fuse together in high-humidity environments, while HPMC capsules are more resistant to moisture changes. If you store your supplements in a bathroom medicine cabinet, that difference could matter over time.