I have a full sheet cake ordered and I am wondering how much foam board would support the cake? Would 4 layers of 3/16" be ok?? The places I went were out of anything thicker!! UG!
Thank you
PS It would be (2) 11x15 side by side

I use the 1" foamcore for that size and it works out great. You might be able to get by with 4 of the 3/16. It should be strong enough to hold the cake but you might get some cracking if you're using B/C icing. You could go on the safe side and get one more 3/16.

If you do use 4 of the 3/16 please let us know how that works. It might actually work better than the 1".

I use the 1/2" thick foam board and it works OK, I order them online by bulk because I use them a lot with my cakes, is a lot chipper than in the store.

I am surprised that 1/2" works for a full sheet cake!! Would you mind sharing your source online? The 1/2" are $6 at Micheals

I use 1/2" foam board for all my cakes and you can see in my photos that I have big cakes. My DH did some research online and found this art supplies store that have them very cheap, we order 30 foam boards for $105 including shipping.
Here is the link
http://www.cheapjoes.com/art-supply/FC398_8744_white-foam-board-thick-x-sheet-pkg-of.asp

I used to order them from Pears art supplies store and they were cheaper than any other store but the shipping for that amount of foam was too hight.

Here is the link
http://www.pearlpaint.com/shop~ocID~500~parentID~500~categoryID~491.htm

Thanks for the help! The (4) 3/16" boards worked fine for the cake. I will use 1/2" next time!