2" Velcro 2 sides. Al Anderson's Source for Sports has a full line of these popular two foot panel, accordian-style, folding mats. These mats are durable, versatile, lightweight and are easy to store. The cover material is an 18 oz. Blue polyester-reinforced vinyl. It is flame and bacteria resistant. The perimeters are double sewn and have a full 2" Velcro fastening system on 2 sides. This allows for the mats to be joined end to end to make a "runway".