Whilst to a certain extent ‘anything will do’ remember that what you use needs to be solid enough to stop artwork from creasing whilst not being so thick or heavy that it moves your package out of the letter rate. Inserts cut from an old cardboard box for example would be ideal weight and strength wise, but make your item too thick to qualify as a letter.
We’ve found that 180gsm card is about right. Much thinner and it seems too flimsy. Thicker is fine, so long as you’re careful about the weight. In theory ordinary 90gsm paper folded in half should be the same weight and be as strong for some reason it doesn’t seem to be though. Getting small quantities of suitable A5 card can be problematic. If you also have other uses for it you could use A4 folded in half, though obtaining small quantities is still a problem.
Paper Cutz, a paper and card specialist we use, and who provide excellent service, will supply:
|25 x A5 220gsm White Card|
|25 x A5 180gsm Coloured Card
|50 x A4 180gsm White Card