Q. Kevodo Nero Yair. 39 melochos mentions it is permitted to use Velcro closings on Shabbat clothing. Does Horav Miller Shlit”a agree?
A. Shemiras Shabbos Kehilchoso (15:78). rules that it is permissible to use Velcro on Shabbos. Velcro is described as essentially the hooking and biding of strands on the one piece through loops on the other. Even if eventually some strands do in fact tear, they are an insignificant few, and besides, they are not designed to tear.
Velcro does eventually wear out, yet only after a long time of use. An analogy is given would be similar walking across a lawn on Shabbat. Even though an occasional piece of grass may be uprooted when you walk over it you certainly didn't intend to uproot it. Since it is not certain that a strand will tear, it is not forbidden to use Velcro on Shabbat.
Just to give you a sense of how Velcro has become a part of Shabbat fashion, Rabbi Twerski of Milwaukee, who is the scion of a Chassidic dynasty, has a gartel (ceremonial belt worn during prayer) that is fastened by Velcro. And who said that Chassidic clothing is straight out of the 18th century!!!
Rabbi A. Bartfeld as revised by, Horav Yaakov Hirschman, Horav Dovid Pam, Horav Aharon Miller, Horav Chanoch Ehrentreu and Horav Kalman Ochs Shlit’a