Ninepeak Hook & Loop Fastener Sew-On , 2" Wide, 9 Yard Length (Black)
https://www.amazon.com/dp/B01E7IK12M..._qMREybR0YS8P6
^ This is the velcro we bought. It was the strongest non adhesive stuff I could find. It's important to note that the velcro actually doesn't need to be that strong. Whatever rope it's stitched to is what matters since you don't want to be climbing without a wrap or two anyway.