Aluminum foil has good moisture-proof properties. Although pinholes will inevitably appear when the thickness of the aluminum foil is less than 0.025mm, when observed against light, the moisture-proof properties of aluminum foil with pinholes are much stronger than those of plastic films without pinholes. This is because the polymer chains of plastics are widely spaced apart from each other and cannot prevent water vapor from penetrating.
Moisture permeability of aluminum foil and plastic films
When the thickness of aluminum foil is small enough, pinholes will inevitably appear. The minimum thickness for pinholes is generally considered to be 0.038mm. Due to improvements in rolling technology and materials, this thickness has been reduced to 0.025mm. Tests have also proven that the vent diameter is critical. When the diameter is less than 5um, oxygen and water vapor are not transmitted within the measurable range.