Yes, but the effects don’t last forever. The strength and water-resistant nature of polyester make it difficult to soften the fibers and therefore difficult to stretch. By soaking a 100% polyester t-shirt in a bath of warm water and hair conditioner/fabric softener, it is possible to stretch and reshape the t-shirt to some extent. The key drawback to stretching clothes made out of 100% polyester is that the effects will most likely only last for one wear. Additionally, if you need the shirt to be significantly bigger than it is, you may not be able to successfully stretch it to your desired size.