Sublimation papers are best used on 100% polyester. As far as using them dye sub with cotton: there is a self weeding paper from China that folks are checking out, and I've read there are pre-treatment sprays to help dye sub adhere to cotton in the 5050 blend shirts, but none of the papers or sprays seem to satify most folks enough that folks use them as a regular part of the process.
There are shirts that are cotton with a poly surface also for use with dye sub - the hitch? Expensive.
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