How Waterproof Is My Rain Coat: What Does 5000mm Mean?

May. 08, 2023

If you are buying yourself a new waterproof rain coat and you're not too well versed in the ins and outs of modern day waterproofing technology, you may find yourself coming across a few rather confusing terms. What on earth does 5000mm mean? And 5000gsm? What's the difference? These are just a few of the questions that will be running through your mind.


Not to worry, our guide to waterproof technology is here to help.

Ladies Long PU Rain Jacket

Number, Numbers, Numbers. But What Do They All Mean?


A waterproof garment is measured with two numbers. The first one measures how waterproof the raincoat is. This is measured in millimetres. You will see numbers from 2,000mm up to 8,000mm across our collection to describe to the consumer how dry the coat will keep you. But what does it mean? For example, if a coat were 5,000mm waterproof, a test is conducted where a long tube is placed over the fabric and the tube is then filled with water. 5,000mm or 5 metres (16.4 ft) is how far you could fill the tube before it would start to leak through the fabric. So in theory, you could stand out in the rain until 5,000mm of rain fell before you would start getting wet.


The second number relates to how breathable the coat is. It is expressed in terms of how many grams (g) of water vapor can pass through a square meter (m2) of the fabric from the inside to the outside in a 24 hour period. The larger the number, the more breathable the fabric. For example, if a coat were 5000gsm breathable, 5000 grams of water would be able to pass through a square meter of the fabric in 24 hours.


Waterproof Technology Explained


Behind the lining inside, there may or may not (depending on the season of the collection) be a layer of insulation to keep your body heat in. Next comes a waterproof membrane which is fixed to the inside of the outer layer of material. The outer layer of material is then sprayed with a Teflon coating which helps the outer fabric to bead off as much rain as possible before it seeps down to the waterproof membrane. All of the seams of our coats are fully taped which means that no water can get in through the stitching.


Which One Is Best for Me?


If you are buying a waterproof coat for walking about town or dropping the kids to school, a waterproof rating of 2,000-5,000mm will be more than enough. If you were planning a weekend in the mountains, we would advise a rating of 5,000-8,000mm as the conditions can be much harsher. A high breathability level would not be required for the school run, but if you have hiking in mind, we would recommend a breathability rating of at least 5,000gsm.


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