During SLA printing, specific areas of resin are exposed to a laser which causes them to cure. Once this process is complete the entire part will be cured, so it may not be completely clear why there is a need to post-cure. To answer this question, we have to understand the properties of hotosensitive resin and how it transforms from a liquid to a solid. While in a liquid state, the resin is made up of lots of unbonded monomers mixed with photoinitiators. Exposing this mix to the strong UV light from the laser causes the photoinitiators to react and for the monomers to bond together and form a polymer. This is the primary sla curing stage. The cured resin is a crosslinked macromolecule, which means that every part of it is directly connected to every other part of it. However, after printing there will still be many sections which are not crosslinked to the extent they could be, which affects tensile strength and other properties. UV light can be used to complete the molecular bonding and make sure every crosslink that could be made is made.