GIFSQ Tools · Module 10 — Packaging & Shelf-Life · Tool 182 of 500
Calculate water vapour transmission rate (WVTR) from a cup-test weight gain, test area and time — with the value normalised to a 25 µm film (ASTM F1249).
Try sample values — fills the form with the worked example below.
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WVTR (g/m²/day)
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WVTR at 25 µm (g/m²/day)
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Gain per day (g)
Equation: WVTR (g/m²/day) = weight gain (g) ÷ [area (m²) × time (days)]. WVTR at 25 µm = WVTR × thickness (µm) ÷ 25.
Method: Gravimetric cup method per ASTM F1249 (water vapour transmission rate through plastic film and sheeting using a modulated infrared sensor is the instrumental version; the cup weight-gain calculation is the same). Report the test temperature and humidity with the result.
Assumptions: steady-state transmission; the film is uniform and undamaged; the stated thickness applies across the test area.
Limitations: WVTR depends strongly on temperature and humidity, so values at different conditions are not comparable; the 25 µm normalisation assumes transmission scales inversely with thickness, which is approximate for coated films.
Rounding: WVTR to 2 decimal places; gain per day to 4 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: Gravimetric cup method per ASTM F1249 (water vapour transmission rate through plastic film and sheeting using a modulated infrared sensor is the instrumental version; the cup weight-gain calculation is the same). Report the test temperature and humidity with the result.
Assumptions: steady-state transmission; the film is uniform and undamaged; the stated thickness applies across the test area.
Limitations: WVTR depends strongly on temperature and humidity, so values at different conditions are not comparable; the 25 µm normalisation assumes transmission scales inversely with thickness, which is approximate for coated films.
Rounding: WVTR to 2 decimal places; gain per day to 4 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: A 0.12 g gain through 50 cm² in 24 h: WVTR = 0.12 ÷ (0.005 × 1) = 24.00 g/m²/day; at 50 µm the 25 µm normalised value is 24.00 × 50 ÷ 25 = 48.00 g/m²/day.
Enter values above to see results.
Typical WVTR: high-barrier film under 1 g/m²/day; plain polyethylene 5–25 g/m²/day at 38 °C, 90% RH. Tool 182 of 500 — GIFSQ
