Gemm

Now this is a good question. I think the key to success here is the fact that when you are thrifting you are able to touch the fabric to get a sense of the quality. I have been disappointed in one or two checked/plaid shirts I bought in my early thrifting days that seemed okay but when I actually cut them they were pretty flimsy, so that was a lesson learned. On the other hand, I found a fantastic men's XL bright orange Hawaiian-style shirt with flamingoes on it (you can see them in some of my I Spy quilts) that put the weight and feel of some of my quilting cottons to shame.

I do think durability might also be tied to how worn the shirt is to begin with. I do check collars and underarm areas carefully for clues to this but I believe the most important thing is to really get a sense of the quality of the cotton by lots of handling before you buy. :-)

Edit: I should make it clear that none of the quilts I've used clothing in have "lived" longer than two years, so I really can't say they've been through the wringer much yet! Durability tests usually go over decades, right?