Avoid a wavy buttonhole on stretchy fabric. This demonstration offers two different methods to make sure your buttonholes end up nice and flat even when sewn on tricky fabric like knit.
Buttonhole on Stretch Fabric
Tag: corded buttonhole
Corded Buttonhole
If you need to do a buttonhole on a stretchy fabric, you should do a corded buttonhole for added stability and strength. This tutorial shows you how to tackle one on your sewing machine.