The problem with drymounting to foamcore is you have to cut your window mat to go INTO the printed image. By drymounting, and triming the print edge off, you can leave a matching white border around the prints edge which looks really nice. If you did this with foam board, you would have a nice mat board, but then the glossy surface of the foam board under... and that would look very untasteful and tacky. Also, you cannot sign foamcore. Pencil just wipes off, or leaves a dent where you write, and pen will wipe off also.
Originally Posted by wildbill
Form core is also too thick, so if your storing prints in a portfolio case, it takes up twice the thickness as normal mount board. That means you can only carry 1/2 the number of prints you could if you used proper mat board.
Also, alot of foam core boards are not 100% archival and acid-free. Your prints would be better of mounted on Alpharag Artcare museum board, or similar.
Light Impressions sell's both Westminster Board (which is more expensive then Alpharag, which is better!) and Exeter Board. The Exeter board is rather quite nice. The "Gallery White" looks very nice with cool tone prints, since it is a slight warm/pinkish.