When you shop for winter coats, you are probably going to encounter two different terms: waterproof rating and breathability rating. Understanding what these terms mean can go a long way toward helping you choose a coat that can stand up to whatever winter in your neck of the woods throws at you. Below we explain these two rating systems and which one you need to consider for which types of winter coats you need.
When shopping for a ski jacket, the waterproof rating is a very important consideration. This number is an indication of how quickly your jacket will become saturated and, as a result, how soon it will allow water to penetrate into the interior layers, making you wet. Essentially, it is a measure of how waterproof the jacket is. Waterproof ratings are measure in millimeters, or “mm”.
How is this determined? In a lab, a tube is placed on the fabric and filled with water. The level at which the water starts to penetrate through the fabric is its waterproof rating. The higher the number, the better the waterproofing ability of the jacket. Put another way, a jacket with a high waterproof rating will better be able to repel snow and rain.
A jacket can only legally be labelled as waterproof if it has a rating of at least 1,500mm. Less than that, and they must be labelled as water resistant. Most waterproof jackets are rated between 5,000 and 10,000mm. A jacket with a higher waterproof rating will also likely have a higher price tag.
An indication that a jacket is waterproof doesn’t necessarily mean that it is made of a certain material. There are actually many different materials that can be used to construct a water proof jacket.
What all of these materials have in common is that the fabric contains pores that are larger than sweat molecules, but smaller than water molecules. The result of that is that the fabric does not allow water to penetrate it, but it does allow the body to breathe by allowing sweat to escape. This keeps the wearer warm but not overheated.
Whereas a jacket’s waterproof rating measures how effectively a jacket prevents the wearer from getting wet, the breathability of a jacket measures how well the jacket transfers moisture from the inside of the jacket to the outside. You could say that the breathability rating is the flipside of the waterproof rating.
A jacket that is breathable will prevent water from penetrating the fabric but will allow sweat to escape through the fabric. The result will be that not only will you stay dry and comfortable, you’ll actually be warmer. When your jacket doesn’t allow your skin to breathe, sweat molecules will make your clothing wet, which will make you cold in the wintertime.
Breathability is measured in grams, or “g”. This rating is calculated by finding the Moisture Vapour Transmission Rate, or “MVTR.” The MVTR is an indication of how many grams of sweat per square metre can escape a jacket in one 24-hour period. At the low end of breathability, fabrics will have MVTR ratings somewhere around 2,500g. Fabrics with ratings of 25,000g are consider to be at the top of the range of breathability.