16x20 3/16" Acid Free White Foam Core

acid free foam core is basically a very similar looking product to regular foam board it's just that it's had the acids and the lignans and all the garbage leached out of it so it's never going to harm your art if you're dealing with fine art if you're doing something where it's a poster and it's not going to ever be worth a whole lot of money you can definitely get away with saving a little bit of money and going with the regular foam core but if you're going to do something where it's irreplaceable or it's fine art use acid free foam core the real difference between 18 and 316 is just the thickness that's it basically if you have a really shallow frame here you'll have a lot of depth choose the 18 phone if you've got a frame that has a lot more rabbit depth to it and has all this extra room choose the 316 it's just going to be a little bit more rigid and it's going to do the job