Anyone using flex cuffs should be aware of this method of getting out of them.
Flex cuffs can be defeated with a shoelace, particularly a thick one such as from a work boot. By placing the shoelace under the cuff and moving it back and forth quickly, it creates friction that ‘burns’ thru the plastic. This can be done in as little as 15 seconds.
This was discovered by Mercer County, NJ, who now has a policy of removing shoelaces from all prisoners restrained with flex cuffs.