Quality is everything. In art, it starts with a canvas. With Direct to Garment (DTG) Printing, it starts with a shirt. With an abundance of fabrics and materials for shirts, information is key for an educated choice.
There three types of fabrics: natural fabrics (i.e. cotton, linen, wool, silk), synthetic fabrics (i.e. polyester, spandex, nylon), and a mix of both (i.e. polyblends, tri-blend). Each has its own properties. But certain properties should be taken into consideration when choosing the best fabric for DTG printing.
Inks used in DTG printing are water-based. Natural fabrics do better in printing because they absorb water better. Meanwhile, synthetic fabrics tend to repel water since plastic and oil are part of their composition. Hence, polyester shirts are not the best option.
What about polyblends/tri-blends? They do fair better than polyester since the ink has some cotton to adhere to. However, since it is still partially laced with polyester, a good solid design cannot be expected. There are blends that don't hold ink well over time. When done properly, printing on polyblends can result in an interesting vintage, washed out look. Generally, the more cotton the shirt has, the better.
Cotton is your best bet. However, not all 100% cotton shirts are the same. Some are of better quality than others. The quality of the shirt will translate to the design once it's printed. Go for the softer, smoother ones. Some manufacturers offer ring-spun cotton shirts. These shirts employ a twisting technique that forms very fine cotton fiber ropes. The result is a stronger weave with a softer feel. You must also watch out for fabric consistency. The thickness of the material determines the amount of ink absorbed.
Nothing is ever a guarantee. The important thing is to know what you're looking for. Try different brands. Experiment until you find the best one.