What makes snap-on roll-up reflective bands want to roll up? I have some of those reflective bands that snap around the ankle or arm to increase visibility while riding.  How are they constructed such that they want to roll up?  What's inside them?



(The reason I'm asking is that I want to punch some holes in the end of two bands so I can connect them, probably with zip ties, into one longer band.  The first time I rode with them their urge to curl was so strong that the ends were rolled up and and it was halfway off my ankle when I got back.  I think a longer band will stay on better.  I want to know if I can punch holes without damaging the bands.)
If you were a kid in the 90s, you probably remember slap bracelets. They're basically the same thing. Usually made up of something like a bit of old tape measure (though you can make bistable structures out of many things). 

You can make a slap bracelet by taking a bit of tape measure (say 6 inches) and rolling it up (gently but tightly), with the number side up (i.e. on the outside of the curl). See this video for an example of how to make it. 

For what you want to do (and for riders in general), I recommend getting velcro reflective bands.