Wood wool, known primarily as excelsior in North America, is a product made of wood slivers cut from logs. It is mainly used in packaging, for cooling pads in home evaporative cooling systems known as swamp coolers, for erosion control mats, and as a raw material for the production of other products such as bonded wood wool boards. In the past it was used as stuffing, or padding, in upholstery, or to fill stuffed toys. It is also sometimes used by taxidermists to construct the armatures of taxidermy mounts.

An evaporative cooler is a device that cools air through the evaporation of water. Evaporative cooling differs from other air conditioning systems, which use vapor-compression or absorption refrigeration cycles. Evaporative cooling exploits the fact that water will absorb a relatively large amount of heat in order to evaporate. The temperature of dry air can be dropped significantly through the phase transition of liquid water to water vapor (evaporation). This can cool air using much less energy than refrigeration. In extremely dry climates, evaporative cooling of air has the added benefit of conditioning the air with more moisture for the comfort of building occupants.