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Technical properties

WVTR (water vapour transmission rate)

Also known as: WVTR, MVTR, water vapor transmission rate, moisture vapour transmission rate, moisture barrier

WVTR is the mass of water vapour passing through one square metre of material in 24 hours (g/m²·day); a lower value means better moisture barrier.

WVTR (water vapour transmission rate), also called MVTR, is the mass of water vapour passing through one square metre of packaging material in 24 hours, usually in g/m²·day. Lower values mean better moisture protection.

Why it matters

Moisture makes crisps and biscuits go soft, causes powders to cake and dulls the aroma of coffee and spices. In the other direction, moist products can dry out. WVTR is assessed together with OTR when choosing a barrier structure.

Material trends

  • PE, CPP and especially BOPP are good moisture barriers, even though their oxygen barrier is weak.
  • PET is moderate; OPA and EVOH are poor against moisture and are usually combined with polyolefins.
  • Metallisation improves WVTR markedly, and intact aluminium foil gives the best result.
  • Paper alone offers no moisture barrier.

WVTR depends heavily on test temperature and humidity, so compare like with like. In a finished pouch, seals and closures matter too. Tell your converter where the product will be sold, since humid climates may call for a tighter structure, and confirm with storage trials.

Frequently asked

Is WVTR the same as MVTR?

Yes, both terms describe the rate at which water vapour passes through a material.

Which film has the best moisture barrier?

Intact aluminium foil gives the highest moisture barrier; among plastics, BOPP and metallised films perform well.

Related terms

OTR (oxygen transmission rate)OTR is the amount of oxygen passing through one square metre of packaging material in 24 hours under set conditions; lower means better barrier. BarrierBarrier is a packaging material's ability to stop oxygen, moisture, light, aroma or grease passing into or out of the pack. Metallised filmMetallised film is plastic film coated with a very thin vacuum-deposited aluminium layer, giving a lighter, lower-cost light and oxygen barrier than foil. Shelf lifeShelf life is how long a product stays safe and keeps its quality when stored as directed; packaging is one of its main drivers. BOPPBOPP is polypropylene film stretched in two directions; it is stiff, glossy, a good moisture barrier and a common printable outer layer in flexible packaging.

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