The core functionality of Thermoplastic Polyurethane (TPU) film lies in its exceptional waterproof and moisture-permeable properties—it can block liquid water from penetrating while allowing water vapor molecules (sweat, perspiration) to pass through.
1. Performance Indicators and Standards
- Waterproofness (Hydrostatic Pressure Resistance):
- Indicator: Measures the film’s ability to resist external water pressure, measured in kilopascals (kPa) or millimeters of water column (mmH₂O). A higher value indicates stronger waterproof performance. For example, regular outdoor clothing may require ≥13 kPa, while professional-grade equipment might demand ≥50 kPa.
- Test Standard: Commonly tested using ISO 811 or ASTM D751 (Burst Strength Method). This involves continuously increasing water pressure on one side of the film until water droplets appear on the other side, recording the pressure value at that point.
- Moisture Permeability (Vapor Transmission):
- Indicator: Measures the mass of water vapor passing through a unit area of the film per unit time, expressed in grams per square meter per 24 hours (g/m²/24h). A higher value indicates better breathability and sweat dissipation. Typically, a value exceeding 5000 g/m²/24h is considered highly breathable.
- Test Standard: Two main methods exist:
- Upright Cup Method (Desiccant Method): e.g., ASTM E96 BW. A desiccant is placed in a cup, sealed with the film, and the amount of water vapor absorbed under specific temperature and humidity conditions is measured. Results are closer to actual wear conditions.
- Inverted Cup Method (Water Method): e.g., ISO 15496. Water is placed in a cup, which is inverted and sealed with the film, and the amount of water vapor evaporating through the film is measured. This method is faster and often used for quality control.
2. Working Principle
The waterproof and moisture-permeable properties of TPU film are not achieved through physical pores but rely on the molecular-level action of its hydrophilic chain segments:
- Waterproof: The film itself is dense and pore-free; liquid water cannot pass through due to its surface tension and the film’s molecular structure.
- Moisture Permeable: The polymer contains hydrophilic groups (e.g., -NHCOO-). These groups “capture” water vapor molecules evaporating from the skin on the inside. Then, through the “segment movement” of the polymer chains, the water molecules are step-by-step “transmitted” from the inside to the outside environment.
3. Testing Methods
- Hydrostatic Pressure Tester: Used to accurately measure the waterproof limit pressure of the film or fabric.
- Moisture Permeability Cup: Used within a constant temperature and humidity chamber to measure the moisture vapor transmission rate (MVTR) using the upright or inverted cup method.
4. Applications
Leveraging these properties, TPU film is the preferred choice for numerous high-end applications:
- Outdoor Apparel: Key component in hardshell jackets, ski wear, and hiking pants, ensuring dryness and comfort for outdoor enthusiasts in wind and rain.
- Medical Protection: Used in surgical gowns and protective clothing to block blood and body fluids (waterproof) while allowing the perspiration generated by medical staff to escape, reducing heat stress.
- Firefighting and Military Training Wear: Provides protection in extreme environments, requiring resistance to fire, water, and chemicals, coupled with high breathability to maintain mobility and performance.
- Footwear Materials: Used as waterproof sock liners (booties) to keep feet dry in rainy conditions while preventing internal heat and moisture buildup.
In summary, through its unique physical and chemical structure, TPU film skillfully balances the seemingly contradictory needs of “waterproof” and “breathable,” making it an indispensable key material in the field of high-performance textiles.
Post time: Sep-22-2025