Not all tee shirts are created equally for sublimation
Printing tee shirts is a fun and profitable way to use your sublimation printer. One of the big things to remember about sublimating a tee is that it needs to be polyester.
Now, there are shirts out there in the market that have various amounts of polyester. The less polyester there is, the lighter your transfer will be when you press it. Also, it can fade pretty quickly.
Check out this chart for reference.
With that said, not all polyester shirts are created equally. Even if a shirt says it is 100% polyester and you got a great deal on it at the box store, it doesn't guarantee that the colors will transfer well or that the shirt won't melt. Melted fabric is the worst!
Ideally, you want to get a quality polyester shirt that is made for sublimation. When you purchase from a trusted sublimation blank seller, like Single J's, great care is taken to only offer the best quality shirt for sublimation. They have been tested by pressing a transfer, washed multiple times, and even tested for thickness. (Many poly shirts are a bit see thru)
You can check out Single J's current shirt inventory here: https://singlejs.com/search?q=shirt&options%5Bprefix%5D=last
If you are going to take the time to make a cool tee, make sure you use a blank that will last.