I think that a lot of the difference between the injectable materials depends upon the marketing literature for each of the various products, a slight difference in how long it is expected to last and the cost of the products. For many applications the material used to inject is somewhat interchangeable. For example, there was a lot of previous discussion about the difference between ECMs (Extra Cellular Matirx) such as Cymetra (human derived) and from Acell (porcine derived). When I dug into it, there really was very little difference between the two and this is what Houser also told me. From what I have read, Radiesse does not actually calcify. Although it is based on calcium hydroxylapatite, this does not calcify but resorbs over time. The idea of all of the quality injectable fillers is not really to harden but to provide a "scaffold" (or structure) for your own natural body tissue to grow into. Sometimes it takes multiple injections to grow a sufficient volume. When thinking about this, we have seen some people describe that their injection or implant resorbs. The reality is that they are expected to resorb over time, but the hope is that in the meantime your own body tissue has grown into that scaffold material and thus will remain. How much volume one will be left with depends heavily upon how well the body has replaced tissue into the scaffold. I think that Cymetra is preferred by some doctors since it is organic based and thus seems to be the most natural material.

Below is one good summary of Radiesse:
The primary compound used in Radiesse is pure, synthetic calcium hydroxylapatite particles composed of calcium and phosphate ions. Because these occur naturally in the body, they are inherently biocompatible. Identical in composition to the mineral portion of human bone, these microparticles will slowly dissolve and be metabolized in the same way as endogenous bone fragments from common fractures. CaHA has been used for decades in plastic and reconstructive surgery, orthopedics, otology, ENT, otolaryngology, maxillofacial surgery, neurosurgery, dentistry, and urology. The gel carrier is comprised of cellulose, glycerin and sterile water; all of which are biocompatible and classified as Generally Recognized as Safe (GRAS) by the FDA and are listed in the United States Pharmacopoeia (USP) and British Pharmacopoeia (BP).

Radiesse provides volume by its physical presence, and studies demonstrate a well-defined tissue matrix forms around and throughout the CaHA implant particles identical to the surrounding area. The implant site remains soft and flexible, similar to the surrounding tissue, and does not show any evidence of ossification, calcification, or migration. Areas injected more than once demonstrated similar tissue response and infiltration results as those sites injected only once. Radiesse seems to have a bit more body or substance, and on a volume per volume basis may give more ‘fill’ than an HA product. This means that for most areas you can obtain the same results with either type of filler product, but you will need to use more HA than Radiesse.