A dry adhesive may be defined as a soft solid material that is free from moisture or liquid. Tape or pressure sensitive adhesives (PSAs) are not classified as dry adhesives because they have tack and upon removal from substrates often leave residue on surface.
A good example of natural dry adhesive system would be Gecko. This creature with its setae adheres to substrates with no chemicals involved i.e. it has a dry adhesive system. The gecko adhesion is believed to be attributed to physical bonding (van der Waals forces).
A hook-and-loop fastener, also commonly known as Velcro, may also be classified as a dry adhesive system.