Velcro, a type of cloth fastener, was inspired by nature. In the 1940s, Swiss inventor George de Mestral was walking his dog when he noticed the interesting shape of the cockleburs that had adhered to his pant legs. The cockleburs that the inventor found grew in a series of natural hook shapes that could adhere to animals or people that passed through them. In the case of Mestral's slacks, the soft material they were made of acted as a series of extremely small loops that the hooks of the cockleburs could fit right into. Mestral realized how hard it was to get cockleburs off of clothing, and decided to replicate the fastening mechanism with cloth.
Velcro is made up of two separate sides. One side is made up of stiffened hooks, and the other side is made up of soft loops. Both sides of a strip of Velcro are made of nylon, but the process for making the hooks is different from making the loops. The hooks are created under an infrared lamp, which helps mold them and give them the appropriate stiffness required. The loops are made of matted, nylon fibers that provide the mates to the hooks. This design is extremely simple, yet also very effective, just as with the cockleburrs.
When the two halves of a Velcro strip are pressed together, it brings the hooks in contact with the loops. There are literally hundreds of thousands of hooks and loops in a single strip of Velcro. Not all the hooks will catch in a loop, but enough of the hooks will tangle up with enough of the loops that a very strong bond will form. The more pressure that is applied to the nylon, the more firmly the hooks will catch onto the loops. When sections of Velcro are held under tension (such as the loops in shoes that Velcro strips are pulled through) the bond remains stronger.