Hi! I love making interchangeable elastic headbands (made with fold over elastic). They have served me the best. Here are the instructions:
Cut a piece of elastic (whatever size you need it) generally if you have the head size subtract an inch since it is so stretchy. Here is the general size chart I use.
Newborn to 3 months - 13.0"
3 to 6 months -14.0"
6 to 12 months -15.0"
12 months to 3 years -16"
3 years to teen- 17"
Then you can either sew or hot glue the ends together (a little overlapping).
Cut another piece of elastic (typically the same color) 1 1/2" long. This piece will go around the seam of your headband and is what makes it "interchangeable". Hot glue the ends of the piece around the seam on the inside of your headband.
I sell both wholesale elastic and interchangeable headbands in my etsy shop www.etsy.com/shop/BizeeB
I am also running a promo that if yo like Bizee B Boutique on facebook you get a code for 10% off in my shop as well as the 75th and 150th fan get a free item. Hope this helps!
Bizee B Boutique