In SLA printing, a thin layer of liquid photopolymer is selectively solidified by ultraviolet (UV) activated photopolymerization. After the layer is cured, the build platform moves vertically, exposing the cured layer to a new layer of liquid resin. The process is repeated, with each subsequent layer being selectively photocured until the entire object is formed. To be suitable for SLA printing, the liquid resin must be photocurable and of low viscosity ; these requirements limit the materials available for SLA printing. Despite SLA's ability to produce objects with relatively high resolution and smooth surface finishes, the materials used in this process tend to be glassy, rigid, and brittle.