Tent Waterproof Ratings: What 1,500, 3,000, or 5,000 mm Means

Take a piece of your rainfly, stretch it across the bottom of a tube, and fill the tube with water to 9.8 ft (3 m), well above your living room ceiling. If the fabric holds, the spec sheet can say 3,000 mm. That’s the entire promise of a waterproof ratingThe water pressure, measured in millimeters of water column, that a fabric withstands before water gets through.: a pressure, on a small piece of fabric. It says nothing about a stormy night, a poorly finished seam, or a zipper left partly open.

So this guide reads just that one line of the spec sheet, the one our article on choosing a backpacking tent only skims. It backs up the shelter step in our guide to your first backcountry camping trip, and it answers the question you ask yourself standing in front of two tents: how many millimeters before you can sleep easy?

What a waterproof rating measures

French sporting goods retailer Decathlon defines it as a fabric’s resistance to water pressure, expressed in millimeters, from a test based on the ISO 811 standard [1]. The technical term is “hydrostatic head,” and the Germans say “Wassersäule.” Either way, the number stays in millimeters on the spec sheets cited here, American brands included, so it stays in millimeters in this guide. A 2,000 mm fabric withstands the pressure exerted by 2,000 mm of water [1].

German brand Vaude describes the test: the fabric is stretched under a water-filled cylinder 3.9 in (10 cm) across, and the number recorded is the point where water starts coming through drop by drop [2]. At MSR, the pressure rises until 3 drops get through [3]. ISO 811, whose title refers to resistance to water penetration and a hydrostatic pressure test, is also a reference for the camping tent standard, ISO 5912 [4]. You have to pay to read ISO 811: these details come from the brands that use it, not from its text.

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These aren’t the millimeters from the weather report. A 2,000 mm tent won’t hold out against 2,000 mm of rain, points out the British consumer group Which? [5], and the retailer Scandinavian Outdoor sets the record straight the same way [6]. For a sense of scale, MSR ran umbrella fabric through its tester: 420 mm [3]. Your umbrella keeps you dry with way less than a rainfly, but then it never has to rub against a rock.

1,500, 3,000, 5,000 mm: what the brands say

None of our sources gives a common scale. Vaude and the German magazine OUTDOOR cite 1,300 mm as the DIN threshold for calling a fabric waterproof [2, 7], without saying which DIN standard (DIN is Germany’s standards body), and Swedish brand Hilleberg notes the lack of a test method shared across the industry, which makes comparisons harder [8]. So everyone sets their own benchmarks, and sellers don’t all have the same tents to defend.

The gap goes further than you might think. MSR stands by 1,200 mm rainflies [3, 10] and won’t commit to a single value, since each tent has its own balance of waterproofness, durability, and weight [3]. Decathlon sticks to 2,000 mm on its trekking tents and tarps [1], and Nordisk to 2,000 mm on its LW models [11]. And OUTDOOR’s view is that the number only really counts on polyurethane-coated floors, not on the rainfly [7].

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Why the floor needs more than the rainfly

The rainfly takes the rain. The floorThe waterproof part of the tent that forms the bottom of the tent body., on the other hand, gets squashed against wet ground, and Vaude describes it as exposed to high pressure [13]. Bergzeit runs the numbers: a 183 lb (83 kg) person in European size 43 shoes exerts about 0.22 bar (3.2 psi) standing up, or 2,200 mm, and more than 4,000 mm crouching on the balls of the feet [12]. A 3,000 mm floor would no longer hold, it concludes [12]. That’s a seller’s example, not a standardized test: the pressure depends on the contact area, and nobody digs through a backpack in that position all night.

MSR gives another reason: abrasion. On the Access, the 3,000 mm floor makes up for wear, and floors generally get a thicker coating than rainflies [3, 10]. The two explanations go hand in hand: a floor has to deal with both pressure and wear.

Independent tests look at this too. For the Swiss consumer show Kassensturz, in 2022, a German lab examined ten two-person tents: for four of them, the head of testing expected moisture to come through the floor after about three days on wet ground [14]. OUTDOOR, for its part, wants more than 4,000 mm on a polyurethane-coated floor [7], but finds the number says little about a polyethylene or silicone-coated one, which it prefers to test on a flooded surface, kneeling and jumping [7].

What wear, coatings, and hydrolysis do to the number

A tent fabric’s waterproofness comes from its coatingThe layer of polyurethane or silicone applied to a fabric to make it waterproof., MSR reminds us [10]. And the number on the spec sheet describes new fabric. Hilleberg offers an example: until 2017, the brand required at least 3,000 mm after mechanical rubbing; since then, it has published numbers for the fabric as delivered, like most manufacturers [16]. Its published numbers then jumped, because they were no longer measuring the same thing.

HydrolysisThe chemical breakdown of a coating caused by water, heat, and time. is polyurethane’s enemy. Time, moisture, and heat chemically break down the coating, MSR explains [10], in use as well as in storage [17]. The brand adds that coatings last longer on thicker fabrics [10], and promotes its own Xtreme Shield coating as three times more durable, a manufacturer’s claim [17].

The sun is another story. According to Hilleberg, UV attacks tear strength first, then water repellencyThe property that makes water bead up and roll off a fabric’s surface.: water stops beading, without the fabric being any less waterproof [18]. Decathlon describes the same repellency, which fades with UV and rubbing and can be revived with a spray [19]. Don’t mix the two up: a treatment makes water roll off, and Hilleberg points out that it doesn’t bring back tear strength [18]. None of these brands promises that a spray will give a damaged coating its millimeters back.

Why a very high number doesn’t guarantee a dry night

Which? sees it in its tests: two tents with similarly high ratings can end up one dry and the other with a puddle, because most leaks come through the seams and zippers, not the fabric [5]. MSR adds that a higher number comes at the cost of more coating: the fabric gets heavier and stiffer and, past a certain point, tears more easily [3], which does a rainfly in the wind no favors.

• Seams. The needle punches through the fabric: Decathlon closes these holes with heat-sealed tape [19], MSR with a thread that swells when wet on its tapeless models [10]. Hilleberg admits that a little moisture can get through a seam during a long rain, and then suggests a seam sealer [20].
• Zippers and openings. Nordisk calls its PU tents waterproof, except for the zippers and openings [11]. Which? warns against doors that open inward: the water they hold falls into the tent [5].
• Tension. Nordisk wants the fabric pulled taut for strength and water repellency [11], and MSR counts on a well-tensioned tent to shed water to the ground [21].
• Contact. Pressing against a wet wall can let water through at that spot, Which? warns [5].

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The link with condensation

A more waterproof fabric doesn’t mean a fabric that gets less wet from the inside. Hilleberg points out that its rainflies are neither breathable nor air-permeable, so vapor condenses on them [22]. Decathlon takes the reasoning further: a fabric made perfectly waterproof keeps the sleeper’s vapor inside [19]. So the number on the spec sheet promises nothing against condensation, which comes down to ventilation and where you pitch.

The two do meet in a downpour, though: raindrops hitting the rainfly knock off the condensation clinging to its underside, and the rain seems to come through, Hilleberg explains [22]. Before you blame your 3,000 mm, look at where the water is landing. Erik Gauden lived this distinction during his three days of rain in Brittany’s Monts d’Arrée: nothing through the floor, condensation under the rainfly.

Which waterproof rating to choose for your tent

None of our sources makes this call for you, and I’m not about to hand you a magic number. Here’s how I’d read a spec sheet, using what this guide’s sources say:

The smart move: read two numbers instead of one, the rainfly’s and the floor’s, then ask yourself where the most exposed seam is. And when you get home, pull the tent out of its stuff sack to dry it, because the closet is where the millimeters go missing.

Worth watching

British retailer Mountain Warehouse demonstrates the test on squares of its own fabric: three minutes to watch what this guide describes, the water column rising until the fabric gives way.

The video is hosted by YouTube (Google): nothing loads until you play it, and Google may then set cookies.

Guillaume Hoarau

Camping, backpacking, bushcraft and hiking

Guillaume Hoarau writes for Outfarer about camping, backpacking, bushcraft, and hiking. A survival-skills buff and a collector of vintage field manuals, he loves clear explanations, lists that actually help and other people’s stories, which he tells well.

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