Tack or tackiness in the context of material behaviour is associated with stickiness and may result from adhesive forces between two materials in contact or cohesive forces in a material bridging two substrates.

Tack may influence the behaviour and perception of consumer products, for example, the extrusion of thick viscoelastic products such as toothpaste from tubes or chewing or handling of sticky foods.

It may also be used to assess the properties of a surface and judge whether it is clean or not. Therefore, a qualitative assessment of tack can be made simply through touch or feel.