DSF

noticed a whole lot in our local 99p store, pale yellow, and pale green might be ok for dye sub, then there is a red and a dark blue. neoprene type cases with the material over just like the blanks we get in white, and the good news - no visible stitching

If they are neoprene then they would possibly struggle under the heat for printing. At 99p though could be worth a go.

yep, they are not my sort of thing, just thought others might be interested