From the sound of it, it's not going to get a huge amount of use. Movie nights, events, etc. And, they look easy to make. So, if they have a lot of T-shirts, and if the interior foam holds up OK, they can just rewrap them in new T-shirts as they wear out. I'm sure it'll be fine. Cotton is pretty resilient. I have T-shirts that are more than ten years old and still mostly intact.
