Bind off loosely with hook
To make sure the edge on a knitted garment is elastic you can bind off with the help of a crochet hook.
Bind off as follows: Slip crochet hook through the first st and pull thread through (leave st on needle), make 1 YO and pull through loop on hook, slip crochet hook through the same st again, pull thread through st and through loop on hook, let the st off the needle, slip crochet hook through next st (leave st on needle), pull thread through st and through loop on hook, slip crochet hook through the same st again, pull thread through st and through loop on hook = 2 sl sts in st, let st off the needle.
Continue like this with 2 sl sts in each st until all sts have been bound off.