Updated: Aug 10
Clear white grains indicate pure TPU material, otherwise if it's yellowish or grayish it means either it made of recycled materials or mixed with other different materials. Unfortunately the recycled power doesn't have a great adhesive property and it will crack easily from first wash.
Run your hand through it, it suppose to have powdery feeling and not stick on your hand.
Check the fastness and the surface after curing it, the good quality will give you a strong and even white surface.
Check the the elasticity of the print after you transferred it onto the garment by stretching it and then do a test wash on the highest degree option you have in your washing machine, and finally put it in a dryer for at least 20 minutes. Check the result!
Note: You might get the best quality TPU DTF adhesive powder but still getting cracked prints.
Curing the powder is a crucial part of the process, as the powder is the glue which helps the print to stick onto the garment.
If you sprinkle the powder manually on the print make sure that every inch of the print will have an adequate and even amount on it and make sure to follow the supplier instructions for the curing process.