Flame treatment is the application of a gas flame to the surface of a material to improve adhesion.

Polyolefins, especially polyethylene and polypropylene bond poorly, because they consist of long non-polar molecules. Without special treatment, adhesives, ink, and other coatings cannot be applied to these materials. By rapidly applying intense heat to a surface, molecular chains are broken and polar functional groups are added. Flame treatment also burns off dust, fibers, oils, and other surface contaminates.

Flame treatment is faster than corona treatment, but requires more complicated and expensive equipment.