Velcro is a brand name of fabric hook-and-loop fasteners used for connecting objects.
The hook and loop fastener was invented in 1948 by Georges de Mestral, a Swiss engineer. The idea came to him after he took a close look at the seed pod burrs which kept sticking to his dog on their daily walk in the Alps. De Mestral named his invention "VELCRO" after the French words velours, meaning 'velvet', and crochet, meaning 'hook'.
Hook and loop fasteners consist of two layers: a "hook" side, which is a piece of fabric covered with tiny plastic hooks, and a "loop" side, which is covered with even smaller and "hairier" plastic loops. There are many variations to this which include hooks on both sides, for example. Some folks call the two sides "posi-cro and neg-cro," but no one is sure which is which. When the two sides are pressed together, the hooks catch in the loops and hold the pieces together. When the layers are separated, the strips makes a telltale ripping sound. The term VELCRO is a registered trademark in hundreds of countries. Generic terminology for these fasteners includes "hook and loop" and "touch fasteners."
The strength of the hook and loop bond depends on how well the hooks are embedded in the loops and the nature of the force pulling it apart. If hook and loop is used to bond two rigid surfaces, e.g. auto body panels and frame, the bond is particularly strong because any force pulling the pieces apart is spread evenly across all hooks. Also, any force pushing the pieces together is disproportionally applied to engaging more hooks and loops. Vibration can cause rigid pieces to improve their bond.
When one or both of the pieces is flexible, e.g. a pocket flap, the pieces can be pulled apart with a peeling action which applies the force to relatively few hooks at a time. If a flexible piece is pulled parallel to the plane of the fastener surface the force is spread evenly as with rigid pieces.
Two ways to maximise the strength of a bond with one or more flexible pieces are:
- increase the area of the bond, e.g. long purse straps.
- ensure that the force is applied parallel to the plane of the fastener surface, e.g. bending around a corner or pulley. For example, shoe closures can resist a large force with little bonding area by wrapping a strap through a slot which reduces the force on the fastener by ensuring the force is parallel to the plane of the fastner and by halving the force on the bond by acting as a pulley system.
Disadvantages and advantages
Hook and loop fasteners have several deficiencies: they tend to accumulate hair, dust, and fur in the hooks after a few months of regular use and the loops can become elongated or broken. The hooks and/or loops can also wear off after a long time. It often becomes attached to articles of clothing, especially loosely-woven items like sweaters. Additionally, the clothing may be damaged when one attempts to remove the fastener, even if they are separated slowly. The tearing noise made by unfastening a hook and loop fastener makes it inappropriate for some applications, but is useful against pickpocketing.
The strength of a hook and loop bond depends on how much surface area is in contact with the hooks: full-body hook and loop suits have been made that can hold a person to a suitably-covered wall.