Pressure sensitive adhesives (PSAs) comprise of systems where the adhesive exists as a thin layer of material normally supported on an inert substrate (celluloid, polyester, polyimide etc). The adhesive does not cure but rather exists as a sticky semi-solid film which requires the application of pressure after application to ensure a good bond is achieved.
Due to the semi-solid nature of the adhesive, increase of adhesion takes place over time as the adhesive slowly wets out the substrate surface, pressure accelerates the early part of this process. The time delay explains why temporary PSA systems eg masking tape often will have a stated maximum application time after which the tape will be difficult to remove cleanly.
PSA systems are used for an extremely wide range of applications and come in many forms ranging from repositionable Post It® notes to those designed to survive long periods out of doors (double sided tape used to in the construction of road signs). The tapes can be single or double sided and can even exist in an unsupported form where there is no carrier film.