Waterproof Breathable Fabrics 101
There is a lot of difficult to decipher terminology regarding waterproof/breathable fabrics and it can be hard to figure out what construction method might be best for you. The following information is basic yet valuable information that will aid you in making an educated purchase.
Construction 101: 2, 2.5, and 3-layer Fabrics
If you read about waterproof breathable fabrics, you've likely heard that they can be constructed using 2, 2.5, and 3-layer designs, with each offering their own subtle advantages. Most rain pants we tested feature 2.5 or 3-layer designs, even if they all might look like a single layer of fabric when you grab them off the rack at the store. You might wonder why does it look like one layer, even if it's labeled as 2.5? This is because the layers are tightly bonded together to function as one. This is true of both 2.5 or 3-layer designs (appearing as one layer), with 2-layer designs featuring an inner hanging mesh of some kind.
All three of these designs share most of their construction qualities with the primary difference found on the inside of the garment. All three styles have an outer shell material, commonly referred to as a face fabric, which is coated with a chemical-based Durable Water Repellent finish (AKA: DWR) to keep the outer most layer from absorbing water. The middle layer (or second layer) is the actual waterproof breathable layer (whether Gore-Tex, another membrane, or coated fabric). Universally, the waterproof layer is located beneath the outer face fabric; this means you can't actually see the waterproof layer from the outside. The third and inner most layer is where the differences lies (between the three construction types).
Both 2.5 and 3-layer fabrics both feature an external DWR treated face fabric and a waterproof breathable membrane in the middle. The functionality of both of the inner most layers is the same: to keep sweat and oils from clogging the microscopic holes (sometimes called pores) in the waterproof breathable layer, which would reduce breathability and potentially make the user feel wet from the inside. The difference is 3-layer fabrics tend to use a more durable polyurethane (PU) film or similar backing, whereas 2.5-layer garments use an exceptionally thin polyurethane laminate or similar coating that is typically "painted" or printed on. This is considered a half layer, even if it covers all of the surface area on the inside.
Three layer fabrics tend to be more durable overall, as the inner most piece of fabric protects the pores in the waterproof membrane from clogging, thus maintaining better breathability between washings. That said, not all 3-layer pieces are more breathable and are often heavier than many of their 2.5 layer counterparts. 2-layer fabrics can also sometimes feel marginally clammier because the inner most layer is a loose hanging mesh that frequently doesn't do quite as good of a job of "absorbing" and transferring sweat away from the user's body. The advantages of 2.5-layer pants are that they are typically lighter, more subtle, and more packable.
Waterproof Breathable Insert Materials
Not all waterproof-breathable fabrics are created equal. While they are all waterproof, they can vary greatly in breathability and in longevity. To summarize, we found that models featuring Gore-tex PacLite offered the best breathability and longevity, but not by a landslide. The propitiatory fabrics used in the Mountain Hardwear Stretch Ozonic and REI Talusphere moved moisture and breathed well, offering respectable longevity.
Durable Water Repellent (DWR)
Durable Water Repellent (DWR) refers ONLY to the chemical treatment that has been applied to the exterior fabric and not to the membrane or coated waterproof fabric that is actually laminated to the inside of this exterior fabric. DWRs primary function is water resistance; this happens as the treatment creates a low surface tension, allowing the water to bead. The goal of DWR is to help keep the external face fabric from becoming saturated, which affects breathability, giving the user a sensation of dampness. All waterproof breathable fabrics feature a DWR, as well as nearly all water-resistant textiles which can be found on insulated and softshell pieces. Most manufacturers use fluorocarbons or fluoropolymer chemicals that are applied and subsequently bonded to the outside of the exterior fabric.
What is Waterpoof?
What is waterproof? A simple answer would be " it won't let any water through the fabric". However, the difficulty lies the fact that water can have variable amounts of force behind it, which conversely alters what it can let through. As an example, concrete can be cut using highly pressurized water, but most people would still consider concrete waterproof. Let's offer some perspective. Most rain generates around 2-3 PSI (PSI = pounds per square inch) of force. Rain in a severe storm (such as 80+ mph winds that might be found in a hurricane) can produce driving rain with forces up to 10 PSI.
A manufacturer recently calculated that a 180 pound person creates around 8 psi sitting on the wet ground and 16 psi while kneeling. While the outdoor recreation industry has no official standard, the US Military requires that for a fabric to be waterproof, it must be able to resist 25 PSI of water. Consequently, that has become a non-mandated guideline that most manufacturers have used. You might be wondering: what do these numbers even look like? To generate three pounds per square inch of force, imagine that a one inch by one inch box, which would have to be over seven feet high and filled with water, was placed on a given fabric in order to generate three PSI.
Considerations by Activity
Folks looking for rain pants to use while day hiking or trail running should focus on low weight and compressibility over other features. The reason is most day hikers are likely to be more selective about which days they spend on the trail; for perfect days, most folks likely won't even carry a pair. However, for marginal weather days or when the threat of afternoon thunder showers is greater than having a pair in the bottom of your pack, a pair can be essential. Many of the "extra features" will likely mean less benefits, as it will simply add weight, as many of these folks will carry a pair of rain pants in their pack as a just-in-case layer".
Backpackers should still focus on weight, though a few extra features and comfort are more important factors. Backpackers might be pickier in regards to the weather, but for most people, especially if it's a few days backpacking trip, they are still apt to go, even if the weather is less than ideal. That means comfort under a hip belt and features to keep the wearer's pants from prematurely inching down can be nice. Weight and compressibility are still important, as even the most diehard backpacker will hopefully be carrying their rain pants more frequent then they wear it. Durability is a factor, but most backpackers follow relatively well-maintained trails that aren't too brushy, making it less of a factor than with other user groups.
Climbing and Mountaineering
Climbers and mountaineers tend to be one of the harder user groups on their gear, particularly rain pants, as they are more likely to wear them much more frequently for a multitude of reasons, such as wind protection or colder temperatures, or to assist in (intentionally) sliding down the mountain after an ascent. Having full or three-fourth length side zippers is of greater value because of the zipper's ability to enable mountaineers to don, or remove their shell pants over larger volume boots (with the potential to be wearing crampons). Climbers not only wear their pants more frequently, but they often wear them in rougher terrain - both in the act of climbing itself, but also often to embark on more off-trail travel in general. Due to the nature of climbing, having better mobility is also of greater value. While you don't want heavy rain pants, you do want them to last more than a handful of trips and to be easy to pull on over your mountain boots - or while roped together on a glacier or on a cliff.
Winter sports can include a wide range of activities, from snowshoeing to backcountry or cross country skiing. Winter sports can include ice climbing. Our recommendations tend to be for the previously mentioned activities, as we would mostly lump these users in with our climbing and mountaineering recommendations. The pants we selected here work OKAY for backcountry skiing, but have more of a hiking/backpacking/mountaineering design focus. The main reason they don't offer incredible performance for backcountry skiing or snowboarding is because most of the models we included are too tight to be pulled over a ski or snowboard boot, while others do not offer the necessary level of breathability.
Snowshoers, like climbers, tend to wear their shell pants far more often; thus, for these users, features, comfort, and durability tend to be weighted slightly more than compressibility or weight. Full or three-fourth length side zippers that allow for easy on, easy off changes, as well as the ability to ventilate on the fly.