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Fabrics and waterproofing

MVTR

Also called moisture vapour transmission rate, breathability rating

What is MVTR?

MVTR measures how much water vapour passes through a fabric in a day, given in grams per square meter per 24 hours. Higher numbers mean a more breathable fabric, with most hiking shells landing between 10,000 and 25,000.

MVTR at a glance

Units
g/m2/24h
Typical hiking shell
10,000 to 25,000
Comparable across brands
Not reliably

How MVTR is measured

Take a square meter of fabric, measure how many grams of water vapour cross it in a day, and you have MVTR. It's the counterpart to hydrostatic head: one number for keeping water out, one for letting sweat out.

Why the numbers are not comparable

The problem is that there isn't one test. Several methods exist, they produce different numbers for the same fabric, and brands rarely state which one they used. That makes cross-brand comparison much shakier than the tidy figures imply, and it's why RET, which has a single ISO method behind it, is the more trustworthy number when a brand publishes it.

Reading it as a band

Treat MVTR as a rough band rather than a precise value. Under about 5,000 is barely breathable. Around 10,000 is adequate for steady hiking in cool weather. Above 20,000 is what high-output shells claim. And no rating overcomes humid air, because vapour only moves towards drier air than the air it's leaving.

What this means when you're choosing

  • Whether the test method is stated, without which the number is not comparable
  • An RET figure instead, which has one method behind it
  • Consistency: a brand quoting MVTR for one jacket and nothing for another

The common mistake

Comparing two brands' MVTR figures

There are several test methods and they produce very different numbers for the same fabric. A brand quoting the most generous method looks twice as breathable as an identical fabric measured another way. Treat it as a band, or use RET.

Common questions

What MVTR is good for a hiking jacket?

10,000 g/m2/24h upwards for general hiking, and 20,000 upwards if you work hard in your shell. Bear in mind that the test method isn't standardised, so a difference of a few thousand between brands means very little.

Is MVTR or RET more useful?

RET, when it's published. It has a single ISO test method behind it, so the numbers actually compare. MVTR is far more commonly quoted, which is why you end up reading it more often.

Where this is defined

Where this comes up

Guides on Tom's Hiking where mvtr changes which product is right for you.

Going deeper

More in fabrics and waterproofing

DWR

DWR is a chemical finish applied to the outside of a rain shell so water beads up and rolls off instead of soaking into the face fabric. It wears off with use and washing, and reviving it is routine maintenance rather than a repair.

Waterproof-breathable membrane

A waterproof-breathable membrane is a thin film bonded inside a shell fabric with pores small enough to block liquid water but large enough to pass water vapour. It's what makes a rain jacket different from a plastic poncho.

Gore-Tex

Gore-Tex is a brand of waterproof-breathable membrane made by W. L. Gore & Associates, and the name most people know the technology by. Gore licenses it to clothing makers under strict construction rules rather than selling finished garments.

ePTFE

ePTFE is expanded polytetrafluoroethylene, the microporous film at the heart of the original Gore-Tex and several competing membranes. Stretching PTFE creates billions of pores per square inch that block liquid water and pass vapour.

Hydrostatic head

Hydrostatic head measures how much water pressure a fabric holds before it leaks, expressed as a column height in millimetres. A 20,000 mm rating means a 20-meter column of water sat on the fabric before the first drops came through.

RET

RET measures how much a fabric resists the evaporation of sweat, tested under ISO 11092. It runs the opposite way to most ratings: lower is better, with under 6 counting as extremely breathable and over 20 as barely breathable at all.

Wetting out

Wetting out is when a shell's outer fabric absorbs water instead of shedding it, because the DWR finish has worn off. The membrane still blocks rain, but breathability collapses and the jacket feels like it's leaking from the inside.

Seam tape

Seam tape is a waterproof strip heat-bonded over the stitch line inside a garment or tent. Every needle hole is a hole in the waterproofing, so a shell with an untaped seam leaks there regardless of how good the fabric is.

2L, 2.5L and 3L laminates

These describe how many layers are bonded together in a shell. 2L has a loose liner hanging inside, 2.5L prints a protective pattern straight onto the membrane, and 3L bonds a fabric backer to it. Durability and next-to-skin feel go up with each step.

Denier

Denier is the weight in grams of 9,000 meters of a yarn, written as a number followed by D. It describes how thick the individual threads are, so higher denier usually means a heavier, tougher fabric, though weave and material matter too.

Dyneema Composite Fabric

Dyneema Composite Fabric is a non-woven laminate of UHMWPE fibers sandwiched between polyester films. It is waterproof from the moment it is made, does not stretch or sag when wet, and is the lightest shelter material in common use, at several times the price.

Ripstop

Ripstop is a weave with thicker reinforcing threads laid in at regular intervals, forming the faint grid you can see on tent and pack fabric. The grid does not stop a tear starting, it stops one that has started from running across the whole panel.

Silnylon

Silnylon is ripstop nylon impregnated with silicone on both faces, the standard fabric for lightweight tents and tarps. It is strong and cheap for its weight, and it stretches when wet, which is why a silnylon shelter sags overnight and needs retensioning.

PU coating

A PU coating is a polyurethane layer applied to the inside of a tent, pack or stuff sack fabric to make it waterproof. It is cheap, takes seam tape well and is what most budget shelters use, and it breaks down with age in a way silicone does not.

Cordura

Cordura is a brand of high-tenacity nylon fabric known for abrasion resistance, used where a pack meets rock and grit. It is a specification a mill licenses rather than a single fabric, so Cordura appears in weights from light shelter cloth to heavy pack bottoms.

Softshell

A softshell is a stretchy woven fabric with a brushed or knitted backing that blocks wind and sheds light rain while still breathing hard. It replaces a rain shell on cold, dry, windy days and is the standard fabric for technical hiking pants.

Base layer

A base layer is the garment worn directly against your skin under everything else. Its job is moving sweat off your skin so it evaporates somewhere other than on you, which is why warmth is a secondary consideration and cotton is disqualified.

Merino wool

Merino wool is fine-diameter wool from Merino sheep, spun for next-to-skin clothing at roughly 17 to 19.5 microns. That fineness is what stops it prickling, and it brings odour resistance and warmth when damp at the cost of abrasion life.

Fabric weight (gsm)

Fabric weight in gsm is the mass of one square meter of the cloth, in grams. On a base layer it is the single number that sets the temperature window: about 150 gsm for warm weather, about 200 gsm for three-season hiking, 280 and up for cold.

UPF

UPF, or Ultraviolet Protection Factor, rates how much ultraviolet radiation a fabric blocks. A UPF 30 garment lets about one thirtieth of the UV hitting it through, so it blocks roughly 96.7 percent; UPF 50 lets one fiftieth through, or 98 percent.

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