Guys with polyester boxers and no children are down voting.

Commando it is, well it's been that way for me for a very long time

This is true. Why's it downdooted?

Effect of different types of textile fabric on spermatogenesis: an experimental study A Shafik. Urol Res. 1993. https://pubmed.ncbi.nlm.nih.gov/8279095/

The results were analysed statistically. In the polyester group the testicular temperature showed insignificant changes during the period when the pants were worn (P > 0.05). By the end of the 24 months there was a significant decrease in sperm count and motile sperms, with an increase in abnormal forms (P < 0.001); the testicular biopsy showed degenerative changes. After garment removal the semen character improved gradually to normal in 10 dogs; two remained oligozoospermic. There were insignificant changes (P > 0.05) in hormones during the study.

Polyester is a man-made synthetic material made from oil products, while cotton is a natural and sustainable fiber harvested from cottonseeds