There are two considerations when choosing a hyaluronic acid dermal filler. The more "cross-linked" (this is a medical term that is used to describe how tightly the filler sticks together) a filler is, the longer it lasts and the more support it can give your skin. However – the more rigid a filler is, the more it will be visible under the skin. Softer fillers such as Restylane and Volbella are best for the lip – since there is a lot of movement and the filler must act in a very fluid way.