Naturally, using paper. For the outer covers, I used Paperpatch glossy glue/varnish because it glues and varnishes at the same time, therefore strengthening the cardboard even more. On the inside, I used wallpaper paste, which is cheaper than the Decopatch
glue. The disadvantages are that it takes much longer to dry, the surface that's pasted really absorbs a lot of glue, the paper isn't as rigid/doesn't have the same stretch ne se tend pas as when you use Paperpatch glue, and there are lots of wrinkles.