I have a couple of pairs of stylish sweatpants (nice details, tapered shape, etc.) that I hoped to wear out of the house, but the knees always bag out on them within minutes of wear. To my eye, this looks really sloppy. What am I missing? Is the fabrication the problem? Does everyone have baggy-kneed sweatpants? I've cut the tag out, but I think they're cotton, or mostly cotton.