Two-piece capsules are hard shells which have a clicking mechanism to contain dietary powders. They offer a more consistent dosing amount than powders - anywhere from 150mg to upwards of 1000mg.
Gelatin
Gelatin capsules are most commonly made from collagenous material from primarily bovine or porcine through a process called hydrolysis. Beef based capsules tend to contribute to an improved capsule firmness, whereas porcine capsules offer better clarity. Gelatin capsules tens to dissolve within 20-30 minutes of swallowing.
Gelatin capsules provide a better bioavailability to poorly absorbed and low solubility nutrients. Due to their smooth nature, they are also more easily swallowed, making them a great options for certain groups that have difficulty taking supplements.
HPMC (Hydroxy-Propyl-Methyl-Cellulose)
HPMC capsules have good stability at low humidity levels with low moisture content (around 5%), with a low static charge. They are better suited to highly reactive molecules are there is no cross reaction between the capsule and the contents inside.
Compared to hard gelatin, HPMC is more suitable for moisture-sensitive products, hygroscopic products, and for low relative-humidity applications. As HPMC is not of animal origin, it does not pose a risk of bovine spongiform encephalopathy and transmissible spongiform encephalopathy.
HPMC can be made from either cotton or wood - with only wood being organic. So if you're wanting an organic certification from a body like the Soil Association, double check the technical specification.
Pullulan
Pullulan capsules are a natural, vegan alternative for hard capsules. they are made from an edible polymer with no taste, sourced from a fungi that has been grown on starch. Their oxygen barrier can be up to 300 times better than HPMC capsules, resulting in a superior protection of nutrients from oxidation, thereby improving stability giving a longer shelf life. They are crystal clear, giving a high visual appeal.
Coloured
Okay, we know this isn't a 'type' of capsule - but it is style a style of capsule to consider. A lot of powder formulations become a standard brown colour, due to the number of ingredients that are blended together. If this doesn't suit with your brand, you can choose to go for a coloured capsule which matches your preferred colour scheme. Coloured capsules can be either monotoned or two toned, with the latter giving a more pharmaceutical look.
The alternative to coloured capsules would be to use wither natural or artificial colours. these can come form many different materials, including ingredients that can contribute to the nutritional content of your capsule such as beetroot powder or turmeric root powder.