The beauty of using your own fat for buttock augmentation is that you are simply increasing a tissue layer that is already present. This means that the buttocks will both look and move naturally after surgery. It may initially feel quite firm and tight right after the fat injections but this softens by a month or so after surgery. The issue with buttock fat injections is not whether a natural result will be created but how much of the injected volume will survive and become permanent.
Web reference: http://www.eppleyplasticsurgery.com/buttock.html