Another material for cooling and flattening is glassine, you can buy in a roll about a meter long and cut up. I have a dozen or so "folders" of this stuff (for each print size) that I use to put one print into each, then the board on top and bottom. This puts 2 layers of the glassine between each print, and the prints can be stored in the glassine folders till mounting, inside old paper boxes or 10 sheet packs. They stay flat till framing. I was told by an art conservator that this is good material for this.