The stiffness of a dermal filler, or its ability to return to its original shape when acted on by forces, is called the G’. The higher the G’, the stiffer the gel. Each hyaluronic acid product takes a different approach to reach a specific G’, with some products focusing more on the extent of the crosslinking while others focusing more on the concentration of hyaluronic acid particles in the gel.

For example, softer hyaluronic acid fillers such as Restylane Silk© are often used more superficially or in areas with thinner tissue overlying it, such as the tear troughs, due to its lower G’. In contrast, Restylane Lyft© has a high stiffness, or G’. As a result, it is generally placed deeper and in areas requiring a more pronounced, stable lift, such as the cheeks or temples.

The extent of crosslinking and concentration of hyaluronic acid gels also determine the product’s cohesivity, which determines whether a product maintains projection or falls apart with pressure, such as massage. A less cohesive product is more malleable and can be massaged in place more easily. Restylane products have the lowest cohesivity of the different brands of hyaluronic acid fillers (2).