The rigid materials we have Aluminium, Dibond and Sintra are intended for independent hanging and therefore can come with a brace. Materials such as archival foamcore, museum board and 3mm Sintra are intended for support within a frame as they are not rigid enough to keep flat even with a brace.
Non archival foam core is intended for short term exhibition and display or informational or non art pieces. Where longer term stability isn’t important and 0.5″ fomacore has excellent dimensional stability. It will not warp or bend.