Strength of Velcro

Why is some velcro very strong while other velcro is very weak?

———- from Ken F of Lincoln. NH

The strength of a given piece of velcro can easily be determined by the tearing sound it makes when ripped apart. A rich, hearty rip means the velcro in question is relatively young, still excited by its work, and intensely attracted to its companion, also a strip of velcro. A weak, listless hiss signifies an older piece, probably over 40, stuck in a dead end job with no sex life and no prospects of finding one. This latter strip knows it’s only a matter of time before it’s replaced by a zipper.