Coir or coconut fiber is fiber from the husk of coconuts. Among other uses, it is used as a natural bedding material.
Generally, coir is used in the middle and upper layers of mattresses to provide support or responsive softness by adding more or less density of material.
Those that are allergic or sensitive to foam, may find that this all-natural, non-toxic material is a good addition. It is important to note that coir mattresses may also have additives: such as cotton, wool, or foam so it is important to do your research to make sure those materials are safe.
Pros: Eco-Friendly, non-toxic, and all natural bedding.
Cons: Comfort is dependent on the craftmanship and quality of the coir material. Low quality bedding can be quite uncomfortable.
Gel is a recent newcomer to the mattress space. It is being used as both a standalone layer and an infusion into foam. Gel benefits mattresses by retaining less heat than memory foam. Also, newer gels compete against memory foam by being more responsive and less toxic.
Gel is similar to foam because it is a polymer made by blending plastics and other chemicals.
Because of gel's heat diffusing properties, it is generally found in the top layer of the mattress under the cover.
Pros: Cooler sleeping surface vs memory foam. More responsive feel when not combined with foam.
Cons: Similar to foam, it is a synthetic blend of chemicals.