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T7 · Transport / BarrierPlastic Packaging EngineeringGATE 2027 Syllabus (XE5)Shop-Floor Standard
Water Vapor Transmission Rate (WVTR) Through Barrier Films
Calculates the steady-state water vapor transmission rate (WVTR) across a barrier packaging film under specified relative humidity and temperature gradients (ASTM F1249 / ISO 15106).
Mathematical Canonical Relation
Plain Formula: WVTR = (P_H2O * Delta_p_H2O) / l
Live Engineering Parameter Solver
Input your production or test values below for instant, verified output.
Verified Engine
film_wvtr
Range: 0.05 – 25 g/m²·day
pouch_area
Range: 0.01 – 0.5 m²
shelf_days
Range: 10 – 730 Days
Calculated Engineering Result:
6.12 grams H2O
Engineering Verification:Daily moisture ingress: 0.0340 g/day.
When & Where to Apply
Use when engineering moisture barrier films for pharmaceutical blister packs, snack packaging, and desiccated electronic moisture-sensitive components.
Common Engineering Pitfalls
- Confusing OTR (Oxygen Transmission Rate) units with WVTR (Water Vapor Transmission Rate) units
- Ignoring temperature dependence (WVTR approximately doubles every 10°C temperature rise)
Physical Assumptions & Validity Limits
- Steady-state Fickian diffusion with constant permeability coefficient
- 100% relative humidity on upstream side and 0% on downstream dry sensor side
- No pinholes, micro-voids, or flex-crack defects
Variable Symbols, SI Units & Dimensional Specifications
| Symbol | Variable Meaning | SI Unit | Typical Industrial Range |
|---|---|---|---|
| WVTR | Water vapor transmission rate | g/(m²·day) | — |
| P_{H_2O} | Water vapor permeability of polymer | g·mil/(100 in²·day) or g·mm/(m²·day) | 0.08 |
| l | Film barrier thickness | μm (microns) | 25 |
Worked Industrial Numerical Example: Biaxially Oriented Polypropylene (BOPP) 25 μm Moisture Barrier
Problem Statement:
A metallized BOPP film has thickness l = 25 μm and water vapor permeance coefficient producing WVTR = 0.85 g/(m²·day) at 38°C / 90% RH. Calculate moisture ingress over 180 days across a 0.04 m² pouch.
Step-by-Step Numerical Solution:
- Calculate daily transmission: 0.85 g/(m²·day) * 0.04 m² = 0.034 g/day
- Multiply by shelf life: 0.034 g/day * 180 days = 6.12 grams of moisture
Final Answer: 6.12 grams moisture ingress
💡 Engineering Interpretation: The 25 μm metallized BOPP barrier successfully limits moisture ingress to under 6.5 g, maintaining crispness and preventing rancidity for dry snack shelf life.
Authoritative Technical Reference & Source Provenance
Plastic Packaging: Properties, Processing, Applications, and Regulations by Susan E. M. Selke & John D. Culter (Hanser, 2016), 3rd Edition, Page 240-248.
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