Rainwear Science 101
The good news: Textile engineers have developed advanced techniques for testing a membrane’s breathability— that is, the rate at which moisture vapor moves through a fabric—which helps companies measure and improve performance. The bad news: No one agrees on which method is best, and brands tend to use tests that show their products in the most favorable light (surprise!). So when you shop for raingear, you’re going to see catalogs, hangtags, and websites promoting various numbers that are meaningless if you don’t understand the tests. Here’s a quick primer to help you decipher the performance claims.
>> MVT (moisture vapor transfer) test: This measures how much moisture (sweat) vapor moves through a membrane in a given time period. The higher the number, the better the performance. How it’s done: The material is stretched over a cup (though even this changes: inverted cup, upright cup, membrane touching—and not touching—the water), then the volume of evaporated water is measured.
>> RET (resistance to evaporative transfer) test: Also known as the “sweating hot plate test,” this measures how much a fabric resists letting moisture vapor through. The lower the number, the better the performance. How it’s done: The fabric is saturated, then placed over a heated, porous metal plate (intended to mimic human skin), and the volume of evaporated water is measured.
>> DMPC (dynamic moisture permeation cell) test: This test measures how much moisture moves through a fabric at various humidity levels. DMPC results are in graph form: The best results are horizontal lines that show consistent breathability across all humidity levels. How it’s done: Fabric is stretched through a chamber, creating two separate cells. Humidity and pressure are controlled and measured on both sides; proponents say it best mimics changing real-world conditions.
While companies agree on how to measure waterproofness (a column of water is stacked on top of a fabric until the fabric leaks), they don’t agree on what constitutes waterproof. For instance, Gore fabrics routinely rate very high in water column testing (20,000mm or higher—picture 20 meters of water stacked on a membrane). Other companies, like Polartec, believe that that level of waterproofing is overkill, unnecessarily inhibiting breathability. As a result, the company engineered NeoShell to have a 10,000mm rating—and our testers reported no leaks.