Hyaluronic acid (HA), the primary ingredient in both Restylane and Juvéderm fillers, is the unanimous favorite for plumping and shaping the lips. It’s produced naturally within the skin and works well as a lip filler because it attracts and retains water, keeping the lips plump and soft to the touch. HA fillers are also temporary and reversible, giving injectors and patients peace of mind.

While the bulk of lip-filling formulas share HA as a common denominator, their individual cross-linking (how the HA molecules are strung together) and chemical characteristics (density, flow, elasticity) are far too nuanced to allow for any sweeping lip-filler generalizations—well, except for one: happy patients always wish the effects lasted longer. Or, at least, as long as advertised, because despite what some products promise, that one-year dream isn’t always realized.