This is called "piling". Like ^ said it happens in friction areas with some materials. Primarily softer feeling outerwear materials. Its something we've been working on since the dawn of time to solve. It's a tough balance, soft comfortable feel with a potential to pill, or stiff crinkly feel and no piling. We think we are getting close to the ultimate solution as we've noticed this happening less and less over the years with our softer feel materials.