"Biofiller" is a general term for any substance that is injected into the skin or subcutaneous areas (just beneath the skin) to help diminish the appearance of wrinkles, thinning of the skin and facial aging. Biofillers such as Collagen, Zyplast, Hylaform and Restylane are all good products, but are rapidly metabolized an removed by the body. Hence, the need for multiple, repeated injections over time.