In industries such as protective apparel, automotive parts, outdoor gear, and medical packaging, waterproof and breathable membranes have long been indispensable core functional materials. However, many procurement officers, designers, and engineers frequently encounter similar issues when selecting these materials: despite specifications indicating high waterproofness and high breathability, practical applications may still result in problems such as water leakage, fogging, lack of breathability, or degradation and failure over time. This demonstrates that the evaluation of waterproof and breathable membranes should not rely solely on individual performance parameters; instead, a comprehensive balance must be considered, taking into account material composition, operating environment, and processing methods.
Below, we provide a straightforward overview of TPU waterproof and breathable membranes from the perspective of material selection.
I. What is a waterproof and breathable membrane?
In simple terms, it is an intelligent polymer film capable of "blocking liquid water while allowing water vapor to escape" -which can be understood as a protective layer with "breathing" properties: rainwater, dew, and larger water droplets cannot penetrate the film, whereas internal moisture, perspiration vapor, or equipment humidity can be released outward through the film material.
It is precisely this combination of unidirectional protection and bidirectional breathability that has enabled TPU waterproof and breathable films to be widely adopted across diverse industries-including outdoor protective gear, medical protective fabrics, automotive electronic sealing, ventilation for lighting fixtures, footwear and luggage materials, construction protection, and precision packaging.
Depending on their structural characteristics, waterproof and breathable membranes are primarily classified into three types: microporous, hydrophilic, and composite. These different structures exhibit variations in waterproof performance, breathability, environmental adaptability, and processability.
II. A balance must be struck between waterproofing and breathability.
A common misconception when selecting materials is that higher waterproofness or higher breathability is always preferable. In reality, the underlying material logic is the opposite: the denser the membrane material, the stronger its waterproof performance, but the available space for gas diffusion is reduced; conversely, larger gas diffusion pores enhance breathability, but diminish both waterproof performance and pressure resistance. If one excessively prioritizes high breathability, both waterproof performance and structural stability may be compromised.
Therefore, for waterproof and breathable membranes, higher performance parameters are not necessarily better; instead, it is essential to identify the appropriate balance based on the actual requirements of the product.
1. Waterproof performance (hydrostatic pressure)
This represents the material's ability to resist water pressure penetration; the higher the value, the more stable the waterproof performance.
The following range may generally be used as a reference:
• Typical daily use scenarios: approximately 3,000–5,000 mmH₂O
• Moderate protection scenarios: approximately 5,000–10,000 mmH₂O
• High-requirement protection scenarios: above 10,000 mmH₂O
It should be noted that the static water resistance of raw materials does not equate to the final water resistance of the finished product; after undergoing bending, heat pressing, lamination, and aging, the water resistance performance of many membrane materials can significantly degrade.
2. Moisture vapor transmission rate / Water vapor transmission rate (MVTR/WVTR)
The breathability and moisture permeability of a product typically determine whether it is prone to feeling stuffy, developing condensation, accumulating moisture, or developing mold.
For products intended for prolonged wear, enclosed use, or exposure to temperature fluctuations, breathability can not only affect the user experience but also impact the service life of the components.
Breathability is commonly expressed as MVTR or WVTR. Since test results can be influenced by factors such as temperature, humidity, and specimen geometry, it is essential to ensure that test conditions are consistent when comparing different materials.
III. Why are TPU waterproof and breathable films widely used?
TPU waterproof and breathable films have been widely adopted primarily due to their excellent overall balance of multiple performance characteristics; compared to other film materials such as PE, PU, and EVA, TPU typically offers the following advantages:
Compared to conventional PE, PU, and EVA films, TPU films offer significant advantages:
• Exhibits good elasticity and toughness, making it suitable for withstanding bending, tensile loading, and deformation;
• Compatible with various processing methods, including heat pressing, high-frequency welding, lamination, and die-cutting;
• Exhibits considerable stability under high and low temperature conditions, with reduced susceptibility to brittleness or deformation;
• Demonstrates promising composite potential with materials such as fabrics, non-woven fabrics, and foam materials;
• It allows for relatively straightforward formulation adjustments to balance waterproofness, breathability, strength, and durability.
However, TPU is not a single, uniform material. The performance of films fabricated from different formulations, varying thicknesses, and different processing techniques can vary significantly.
IV. Different scenarios require entirely different equipment selection.
When selecting a TPU waterproof and breathable film, you should first identify the primary requirements of the product.
① Susceptible to leakage, exposure to rain, or water immersion
Prioritize high waterproofness formulations, appropriately relax breathability requirements, and focus primarily on waterproof stability after bending.
② Sensitive to stuffy, humid conditions; prone to condensation and mold growth.
Prioritizes a high-moisture-permeability formula, balances basic waterproof performance, and focuses on long-term breathability without degradation.
③ Prolonged outdoor use, exposure to extreme temperature cycles
Prioritize TPU formulations with superior aging and hydrolysis resistance; reject materials that offer high performance in the short term but suffer from rapid degradation over extended periods.
④ Requires thermal pressing, high-frequency treatment, and secondary processing
Prioritize process-appropriate TPU films to prevent perforation, deformation, and performance failure after processing.
Many customers choose the wrong materials not because their specifications are insufficient, but because the application scenario is mismatched.
V. Do not rely solely on samples; instead, conduct finished-product validation.
Raw material parameters should only serve as a reference for material selection and cannot fully represent the performance of the final product.
LEO New Materials recommends that all customers adhere to a three-step verification process when selecting materials:
1. Basic raw material testing: including properties such as waterproofness, breathability, thickness, tensile strength, and temperature resistance;
2. Post-processing retesting: Simulate processes such as thermal pressing, lamination, and bending, then observe changes in performance;
3. Operational condition simulation testing: Conduct rain exposure, immersion testing, and high/low temperature testing based on actual application requirements.
Only materials that have passed actual performance testing of the finished product are suitable for mass production.
VI. Conclusion: A high-performance breathable membrane is "matched" through careful selection.
There is no universal "optimal solution" for selecting PU waterproof and breathable membranes; for different products, the key is not to blindly pursue the highest performance parameters, but rather to conduct a comprehensive matching process based on the operating environment, waterproofing requirements, breathability requirements, processing methods, and durability requirements.
Yantai LEO New Materials specializes in the research, development, and customization of functional TPU films. We provide tailored material solutions-such as waterproof, breathable, aging-resistant, and high/low temperature-resistant options-based on customers' specific application scenarios, complemented by sample testing, process guidance, and batch production support services.
