Dear sa6aT9in191:Great question! Collagen is the main structural molecule and protein in the fibers of the skin and its connective tissues. There are 28 or more different types of collagen made into a triple spiral helix in the body's tissues. From conception until about the age of 30, your genes govern the production of collagen for growth (and repair). After the age of 30, collagen is formed to repair injury through a process called inflammation. Inflammation does not necessarily mean red, hot infection. It is the process of healing and structural growth. Inflammation can be stimulated to form "scar" or collagen from injury. Other stimulants of collagen induction include: heat through the skin from lasers, radio-frequency, ultrasound, ThermiTight and other energy forms. Each has its pro's and con's. Sculptra is unique in that "injury" is bypassed by injecting a cell messenger to stimulate the fibroblast to make collagen. Neither of these collagen inducing options forms "volume" per se. Each time heat affects collagen directly, it: tighten the protein then stimulate more lumpy collagen formation during the fibroblastic phase of inflammation and then remodels into a smoother, stronger but different collagen molecule. Sculptra leaves behind a fibroblast stimulator particle called poly-L-lactic acid which provides phases 2 and 3 above for prolonged stimulus for up to a year.Both, therefore stimulate firming or tightening but not really volume formation (unless you define tissue contraction into a smaller volume as "filling"; I don't).I hope this was helpful. Always consult with a Board Certified, skilled Plastic Surgeon to see what is best for you.