Foam Board, sometimes called Foamcore, Foam Core, or Foam Core Board is a necessity for all modern craters or people who need to build structures but require something a little nicer than cardboard. The standard Foam Board for everyday use is 3/16 of an inch thick (or just shy of 5mm). Lots of local stores have it in some quantity. From corner drug stores like Walgreens to Office Supply stores like Staples to Big Box Super-centers like Walmart. Last weekend I needed some Foam Board to build a Mat Board so I went on a trek from store to store looking for the best bargain
My first stop was Walgreens. They had Crayola brand Foam Board for $3.99. Measuring in at 22 inches x 28 inches I knew it wasn't going to be my best bargain so I pressed on. You can see their selection here.
I stopped over at Walmart and they had a large selection of Foam board and at a discount. They had the Elmer's brand Foam Board for $2.97. Measuring in at 30 inches x 20 inches it is technically less Foam Board but at a dollar cheaper the decrease in price more than makes up for the decreased size. I even did the math. At Walgreen you pay $0.0065 per square inch while Walmart charges you $0.0050 per square inch (math rounded for ease of use). You can see what Walmart offers here.
My final stop in the land of Brick and Mortar Foam Board Suppliers was Staples. The carried the same 30 inch by 20 inch Foam Board size as Walmart but instead it was Staples Brand. Oddly enough it was priced the same as Walmart but the price tag said it was originally $3.49. I assume that was just marketing at it's finest. Staples did carry the widest variety of Foam Board. They had it in a variety of colors for an additional dollar or so. You can see what Staples offers here.
I have heard that if you keep an eye out you can find some really cheap stuff at the big craft stores like Micheales or at Dollar stores but the quality may suffer.
Lastly I had to check the Online only retailers to see what kind of pricing they had. I found that the Elmer's Brand EPI900802 Foam Board seemed most closely match what I saw in the stores and was well reviewed. At this moment I see the pricing on the Foam Board is $34.37 for 10 boards. So you can do the math and see that they are more expensive than picking it up in Walmart or Staples stores. I'm sure if you waited and watched promotions you could find a worthwhile coupon code or wait for the price to drop and get it at an additional discount. I also noticed they have Foam Board available in larger sizes and some of the highest quality Foam Board, but as I see it pricing wise online pretty much matches what you can pick up in a store.
If you buy it in a store you have the advantage of picking through the pieces they have on hand and hopefully finding a piece without banged corners or crumbled edges. If you buy online you aren't limited to stock on hand in a store. You can easily buy a thousand or more pieces, and you should see quite a savings at that point. So if you just need a sheet of Foam Board run out to your local Big Box retailer and pick one up. If you have special needs from your Foam Board like an odd size or mass quantity you should shop online.