Ever since Gore-Tex revolutionized raingear in 1973 with the first waterproof/breathable membrane, fabric engineers have been working to improve the breathability half of the equation. As every overheated hiker knows, more is definitely better. And while we’ve seen many incremental advances over the years, nothing compares with the windfall of 2011. W.L. Gore, Polartec, Mountain Hardwear, and Columbia all launched new outerwear lines that employ thinner, more porous waterproof membranes combined with advances in fabrics and laminating techniques that further enhance breathability. The result? Our field testers report that the best new shells are 20 to 30 percent more breathable than anything they’ve used before, meaning you can stay comfortable while working harder in a greater range of conditions. And if you do overwhelm one of these jackets on a hard summit push, sweat disperses—and midlayers dry—faster. So which one’s the best?
We studied countless pages of lab data supporting each brand’s breathability claims (they all tout different test methods, see below), plus dense workbooks detailing the materials and construction methods. The graphs and wonky verbiage provided valuable background, and we’ve summarized the key claims made by each manufacturer in the individual jacket reviews. But as every backpacker knows, you can’t mimic an Arctic maelstrom in a lab. And the breathability of any jacket only starts with the membrane. Real-world performance comes from the sum of the parts, including the breathability of the liner and face fabrics, the glue patterns used to bond it all together (glue doesn’t breathe), and the effectiveness of the DWR (durable water repellent) treatment. The DWR performance is key because it causes water to bead up and roll off; if the fabric becomes saturated, the water itself forms a non-breathable layer.
So we set the graphs aside and put the new shells through four months of hard field testing. By the end, we’d narrowed the field to these four standouts. They each proved extremely close in terms of breathability (scores are for the whole jacket, not solely the membrane), so base your pick on the total package, including features, fit, and packability.
Most Breathable: Mammut Felsturm Half-Zip
Most Versatile: Westcomb Apoc
Most Durable: Mountain Hardwear Jovian
Best Value: Columbia Peak 2 Peak/Peak Power
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.