Polykraft:

Polykraft is a layer of kraft paper laminated to a thin layer of polyethylene film which is factory applied on the metal in a lamination process. It is an improvement from the paint system as Polykraft is 1.5 mil (37.5 μm) thick and uses polyethylene layer which is good for moisture resistance. However, kraft paper exhibits a poor water resistance and can be easily damaged on mechanical abuse. The properties of polykraft deteriorate significantly over a short time. Polykraft promotes the growth of fire, hence is not used in areas where there is a high risk of fire.

Polysurlyn:

Polysurlyn moisture barrier is a 76 μm thick three-layer film which is factory laminated on the metal without the use of any addition adhesive layer. The layers are a combination of polyethylene and Dupont™ Surlyn®. Surlyn® is known for its strength and moisture resistance properties and combining it with 2 additional layers of polyethylene prevents the alignment of pinholes in each layers, hence, this moisture barrier exhibits zero pinholes. Polysurlyn moisture barrier is the most popular moisture barrier used today.