WATERPROOF VS WATER RESISTANT: WHAT'S THE DIFFERENCE?
When the backcountry boffins first started differentiating between water resistant and waterproof a few decades ago, many of us suspected a trick, or at least an over-fussy and finicky distinction that could, for most of us, be politely ignored.
In the interim, the boffins have been exonerated, and their fussiness revealed as symptomatic of the huge strides that have been taken in outerwear technologies in recent years. We slowly, and some of us with tails between legs (this writer included), realized that the distinction made was not only a valid one for scientific reasons, but also one that was pivotal to getting our hands on the correct clothes to wear hiking.
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To help you do the same, this article will bring you a short-and-sweet guide to the difference between water-resistant and waterproof garments.
Water-resistant fabrics do precisely as their name suggests, that is, resist water to lesser or greater degrees. Compared to waterproof varieties of garment, these products are less capable of preventing saturation from rainwater.
Unlike waterproof jackets, the ability of water-resistant varieties to repel moisture relies entirely on a durable waterproof repellent (DWR) coating that is applied to the outer fabric during production. This coating prevents water absorption by a process described in more detail in our guide to DWR waterproof coatings. In a few words, this coating (sometimes also referred to as a “lining”) causes water to bead up on the garment’s surface and run off before saturating the fabric.
DWR ratings are determined by the percentage of fabric with no water sticking to it following a simple spray test. For example, if the DWR rating is 80, then 80% of the fabric was water-free after the spray test. A second figure indicates the garment’s performance in the same spray test after a number of washes. For example, a rating of 90/20 tells us that the fabric maintains a 90-point rating (being 90% water-free in the spray test) after 20 washes.
Waterproof garments usually combine a DWR coating on the outer fabric, fully taped seams, and a built-in membrane lining such as those described in our article on waterproof and breathable fabric (Gore-Tex, eVent, HyVent are a few of the most popular varieties).
A membrane lining is an incredibly thin film or sheet of material with literally billions of microscopic holes which are too small for rainwater to penetrate but large enough for water vapor molecules (from sweat) to pass through in an outward direction. This membrane assists breathability and forms a second, more impermeable barrier after the DWR outer.
The waterproof capacity of any garment is quantified by hydrostatic head ratings, which are covered in more depth in our guide What is Hydrostatic Head? The legal minimum hydrostatic head rating for classification as a waterproof garment is 1,500mm, which we’ll take as a starting point for the summary below.
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Kieran James Cunningham is a climber, mountaineer and writer based in the Italian Alps. He’s climbed a handful of 6000ers in the Himalayas, 4000ers in the Alps and loves nothing more than a good long-distance wander in the wilderness. He climbs when he should be writing, writes when he should be sleeping, has fun always.