Cold mounting is a process where a work on paper is bonded to a flat surface using a double transfer film. This has the advantage of making an image super flat and is used particularly for photographic works. There are many rigid surfaces which are suitable for cold mounting works on paper. Here are some of the more popular materials and some differences between them.
Foamcor: Lightweight and acidfree. Available in different thicknesses but needs to be framed as it's quite soft.
Dibond: An aluminium composit with a recycled rubber centre. Usually 3mm in thickness.
Aluminium: Pure aluminium sheet up to 8ft x 4ft in size .Very lightweight from 1.5mm in thickness.
Foamex: A solid plastic composit board available in different thicknesses.
Note Coldmounting is an irreversible process and is not recommended for one off pieces of work.