Stretch magic rips/breaks when used for a long time. I use fabric-y elastic beading string. They have 5 yard things at Michaels or Walmart for a few dollars. Or Amazon has a 100 yard one.

Also, make sure to use elastic cord, something like this. https://www.amazon.com/gp/aw/d/B000GPTDB6/ref=mp_s_a_1_15?ie=UTF8&qid=1507554123&sr=8-15&pi=AC_SX236_SY340_FMwebp_QL65&keywords=elastic+cord+for+bracelets

When I first started I was using the plastic cord which barely stretches over your hand and snaps more easily. Also, as a guy I was also skeptical but yeah, it's a lot of fun.