The base of most hot melt formulations is a polymer, like EVA (Ethylene-vinyl acetate) or PO (Polyolefin) for packaging hot melts.
For rubber based PSA hot melt adhesives the base is a Styrene Block Copolymer (SBC).
Tackifiers are added to improve initial adhesion and to modify the base polymer.
Tackifiers are an important part in hot melt adhesives on both their cost and performance properties. Tackifiers are usual low molecular weight and are resinous, with the negative side it’s mostly having glass transition temperatures and softening temperatures above room temperature.
These resins provide “tack” and viscoelastic properties in the hot melt adhesive formulation.