Various constructions and strengths are available. Some touch fasteners are strong enough that a two-inch square (5 × 5 cm) piece is enough to support a 175-pound (80 kg) load. Fasteners made of Teflonloops, polyester hooks, and glass backing are used in aerospace applications, e.g. on space shuttles. The strength of the bond depends on how well the hooks are embedded in the loops, how much surface area is in contact with the hooks, and the nature of the force pulling it apart. If hook-and-loop is used to bond two rigid surfaces, such as 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 disproportionately applied to engaging more hooks and loops. Vibration can cause rigid pieces to improve their bond. Full-body hook-and-loop suits have been made that can hold a person to a suitably covered wall.
When one or both of the pieces is flexible, e.g., a pocket flap, the pieces can be pulled apart with a peeling action that applies the force to relatively few hooks at a time. If a flexible piece is pulled in a direction parallel to the plane of the surface, then the force is spread evenly, as it is with rigid pieces.
Three ways to maximize the strength of a bond between the two flexible pieces are:
· Increase the area of the bond, e.g. using larger pieces.
· Ensure that the force is applied parallel to the plane of the fastener surface, such as bending around a corner or pulley.
· Increase the number of hooks and loops per area unit.
Shoe closures can resist a large force with only a small amount of hook-and-loop fasteners. This is because the strap is wrapped through a slot, halving the force on the bond by acting as a pulley system (thus gaining a mechanical advantage), and further absorbing some of the force in friction around the tight bend. This layout also ensures that the force is parallel to the strips.