Foamcore is one of the most popular mounting and frame backing materials for pictures. For the most part there are two concerns when selecting foam core: thickness and archival level. It is most commonly available in either 3/16 or 1/8 inch thickness. Frame Destination sells both for the same cost. We recommend 3/16 unless your frame does not have enough rabbet depth to hold it. 3/16 is less likely to warp and provides additional picture stability for large picture frames. Our customers selling photography in artshows will often use 1/8 foam core mounting board when selling matted only works of art because they take up less space. More will fit in their display bins and they are easier to transport. The second major concern is achievability. Foamboard is generally available in regular and acid free forms. If you are concerned about your print lasting then of course you should use the acid free form. If your primary concern is cost effectiveness then you should use the regular foam board.