Just the thickness! 18pt rigid vinyl and 20pt plastic are both made of Polyvinyl chloride (PVC). Polyvinyl chloride (PVC) is the world's third-most widely produced synthetic plastic polymer, after polyethylene and polypropylene. 20pt is just thicker and stiffer than 18pt. They are both great choices for business cards or menus. The best way to describe paper is to not do so in words, but to see it for yourself! Luckily, both are included in our free sample pack for you to see what suits your needs best. In the synthetic plastic family of papers, we include 8mil synthetic plastic. 15pt synthetic plastic cardstock. 18pt rigid PVC vinyl. 20pt white plastic. 20pt frosted plastic. 20pt clear plastic. So what are you waiting for? Order a free sample pack now! https://www.4over4.com/free-samples