Breathability Guide | What is Breathability?


Thinking of outdoor wear, the first quality that springs to mind is normally waterproofness. Rarely do people – even outdoors enthusiasts at times – think of or consider breathability as a crucial element in the build of their gear. We’re out to prove this attitude wrong in this guide to breathability, and we’re going to find out exactly why breathable attire is the best choice for boosting your active performance outdoors while keeping you as comfortable as can be.


The Definition of Breathability

In a nutshell, breathability refers to the ability of a fabric to absorb moisture and release it through the material itself, allowing it to ‘breathe’. This continuous cycle of motion is at the heart of the mechanism of breathability: the more you sweat inside a breathable clothing item, the higher its perspiring capacity should be, and this circular action never stops.

There are a range of different breathable fabrics on the market and they are sought after for their outstanding usefulness for outdoor, sports and fitness activities. If you’re outdoors, the major concerns you face are keeping warm and dry, but these can sometimes come into conflict with the need to stabilise your body temperature in chilly environments while exercising intensively. Since intense physical activity will hike up your perspiration levels, you might find yourself overheating in this scenario if you’re wearing insulated layers to keep yourself warm – this is where breathable clothing items come in handy.



Across the world, there is no universal, standardised way to measure breathability. However, there are three different tests currently in place which show how many grams of water vapour are able to pass through a fabric in a set time period. These are the ‘Upright Cup’ test, the ‘Inverted Cup’ test, and the ‘Sweating Hot Plate’ test.

Moisture Vapour Transmission (MVT)

Moisture vapour transmission is dependent on the formation of a temperature or pressure gradient between the interior and exterior of the breathable garment. The breathable fabric works by equalling the heat and pressure inside and outside the garment, constantly working to bring them to a balance.

When perspiration arises and the moisture vapour reaches the inner face of the garment, it must pass through the fabric and evaporate on the surface. If its passage through the fabric is blocked, or if the transmission rate is slower than the generation of extra moisture vapour, the vapour will condense on the inner face.

This is why breathable fabrics work best when the air inside the garment is warm and humid, and the air outside is cold and dry to evaporate the excess moisture. If the weather conditions produce an environment external to the garment that is humid and warm, the rate of moisture vapour transmission will be lower and might allow for condensation to build up on the inner face.

When undertaking intensive physical activity and the moisture vapour transmission rate is exceeded, there is an increased chance of condensation forming.

Breathable clothing is better able to prevent condensation build-up the more close-fitting it is. This is due to the fact that moisture vapour on its way out of the breathable garment will come into contact with pockets of cooler air in between the mid- and outer layers, so condensation is more likely to form on the inside of the outer layers.

Resistance of Evaporation of a Textile (RET)

Resistance of evaporation of a textile refers to the level of resistance that a given fabric will demonstrate against evaporation, meaning that the lower the RET, the more breathable the fabric.

Thus, we can say that a RET of 0 is a perfect breathability score while a RET of 30 and over won’t show much, if any, breathable qualities. The table below illustrates the RET spectrum:

RET Score

Breathability Notes

0 – 6 Extremely breathable. Comfortable at higher activity rate.
6 – 13 Good to very good breathability. Comfortable at moderate activity rate.
13 – 20 Satisfactory to acceptable breathability. Uncomfortable at high activity rate.
20 – 30 Unsatisfactory or slightly breathable. Moderate comfort at low activity rate.
30+ Unsatisfactory or not breathable. Uncomfortable and short tolerance time.


The ‘Upright Cup’ Test

This test measures the rate of moisture vapour transmission through the garment. The fabric to be tested is fastened onto an upright, sealed cup in a controlled environment, and after a select period of time the cup is weighed to record how much moisture has passed through the fabric into the cup.

The results are expressed as g/m²/24hrs, indicating the level of moisture the fabric is able to release, and thus its breathability rating.

The ‘Inverted Cup’ Test

This test measures how much water is absorbed by the garment. The fabric to be tested is placed onto a waterproof, permeable membrane and held over an inverted cup in a controlled amount of water. After a select period of time, the cup is once again weighed to determine how much water has been ‘pulled’ into it by the fabric.

The results are also expressed in g/m²/24hrs, demonstrating the moisture vapour transmission rate and quantity, and thus the fabric’s breathability rating.

The ‘Sweating Hot Plate’ Test

This test differs slightly from the ‘Upright Cup’ and ‘Inverted Cup’ tests in that it measures the evaporative resistance of the fabric under test and the moisture loss of a garment when heat is applied to it, simulating the extra body heat generated during strenuous physical activity.

The artificial heat is generated from a heated laboratory metal plate at temperatures similar to those which cause the human body to produce considerable amounts of sweat. The garment being tested is then added to the plate along with water to mimic real-life moisture. The plate is kept at a constant heat, then measured to show the evaporation, or how much energy is being used to keep the plate cool. In a real-life scenario, this happens when moisture vapour is transmitted to the outer layers to keep the body at a constant temperature. The resultant energy is designated as the resistance of evaporation of a textile (RET).


Breathable Fabrics and Membranes

Outdoor clothing and footwear incorporates breathable fabrics and membranes for reasons of performance, so that users and athletes can pursue physical activity of any intensity while remaining comfortable and protected. Breathable micro-porous membranes are made from a thin, man-made film containing tiny pores which are large enough to allow water vapour – or more specifically, sweat – through to evaporate on the surface of the garment but too small to allow water droplets (rain, snow etc.) to pass through.

Breathable membranes are usually laminated to a face fabric and are normally available in two- and three-layer versions. Two-layer fabrics are normally used in lined garments, where the lining protects the membrane. Three-layer fabrics are shell garments and the membrane is sandwiched between an outer and inner layer of fabric.

Breathability ratings for outdoor clothing, footwear and accessories are generally measured using the unit mvp, which stands for moisture vapour perspiration, and refers to how much moisture can vapourise through the fabric.


Tres-Tex® is a specially designed fabric which incorporates properties of waterproofness, windproofness and breathability into one single material. The breathable fabric used in Tres-Tex® garments is ideal for active, highly mobile pursuits as it draws moisture away from the body and lets it evaporate on the surface.


Mesh Areas

Mesh areas are used in clothing and footwear to aid breathability. The very loosely woven fabric has large holes uniformly spread along the fabric to promote venting across the garment or shoe.

Pit Zips

Pit zips are a special kind of zip found under the armpits, and allow you to remain cool if you’re overheating in your layers or due to external conditions. With pit zips, you’re able to release excess heat and moisture without exposing the inner layers of your outfit to the cold, or your skin to the external environment.

If you’d like to learn more about the technology behind Trespass clothing and footwear or read our guide to insulation, keep following our Expert Advice section for the latest tips and hints for the outdoors.

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