The two most popular T-shirt fabrics in the decorated apparel industry are 100% cotton and a 50% cotton and 50% polyester blend. As a commercial screen printer, you should know how to print on both.
Blended fabrics offer some advantages over pure cotton. In general, they have a lighter feel, which appeals to customers in certain climates. The polyester content reduces fibrillation, which can cause a print to look faded because of the little cotton fibers that stick up through the ink.
The main thing you have to contend with when printing on 50/50 blends is dye migration. Dye migration is a process that occurs when polyester hits a certain temperature, 300F. At this point, the dye in the shirt itself sublimates, rising up into the ink layer that you have printed. For example, if you print on a red 50/50 shirt with white ink, you are probably going to end up seeing your ink turn pink.
There's a couple of ways to handle this, depending on the ink type you're using. If you are printing with water based ink, you will want to get Warp Drive Low Cure Additive. You add it into your ink, and it lowers the minimum cure temperature down to 180F, though you can still go as hot as 280F. Then, you let the shirt sit, without washing, for 48 hours to allow the additive to complete the curing process.
If you are printing with plastisol ink, your best bet would be to get a low bleed ink. These inks are made specially so that the dye of the shirt cannot bleed into the ink post-curing. Currently, Ryonet carries Wilflex Epic Perfect White LB. You can also underbase your design with a blocker, like our Wilflex Epic Performance UB Barrier Base.