The fabric’s water resistance index is very important for outdoor people.

“Waterproof index” is one of the most important parameters of almost every Outdoor item made of fabric (Tents, clothes, boots, waterproof bags-backpacks,…), this is also almost the thing that Outdoor people care about the most when choosing to buy items. But not everyone clearly understands its meaning and how to apply it in using waterproof items properly. Below are the main notes you need to know about this index:

1. What is the waterproof index?

The waterproof index of a fabric is usually expressed in “mm” which is equivalent to the level of water pressure that the fabric can withstand before being permeated. Each mm corresponds to the pressure level of 1mm of water column pressed against the fabric for a certain period of time, which means that a fabric with a waterproof index of 1000mm will withstand the pressure of 1 meter of water during the test period (Most manufacturers specify 1 minute as the standard time, however, each brand may use a different test time. That is why 2 types of fabric with the same waterproof index from 2 different brands can have clearly different waterproofing effects).

Procedure for testing fabric’s water resistance index on a pressure machine. Source: Madfoxgear

2. So how much is appropriate?

Even though you understand the mm number that comes with waterproof in the fabric’s waterproof index, it is still difficult to know how much is enough for your needs for those who are new to Outdoor sports. Therefore, FanFan will specify it in the most understandable way, however, the accuracy is only for reference, not absolute.

For example: X is the waterproof index of tent fabric, increase,…

X =< 1000mm: Light rain, heavy fog. Suitable for camping in areas with lots of trees (reduces rain pressure), with a roof or in the dry season.

1000mm < X < 2000mm: Moderate rain, moderate rainfall duration. Suitable for mixed climate, not heavy rain, many trees.

2000mm < X < 3000mm: Moderate rain, heavy rain, long duration of rain. Suitable for rainy season, but the weather should not be too bad.

X >= 3000mm: Heavy rain, drizzle. Suitable for trips in bad weather, or camping by the sea during heavy rain and strong winds.

3. Waterproof life:

This may sound strange to most beginners, but it is true, waterproof fabric like everything else has a lifespan. Especially in hot and humid tropical areas like Vietnam, this lifespan is much shorter than in cold and dry areas.

The reason is that the technology used to make a normal fabric waterproof is not permanent. Most waterproof fabrics on the market use 2 technologies:

– PU COATING: This is a technology that applies a layer of PU glue to the underside (inside/wrong side) of the fabric, creating a sealed membrane that makes the fabric waterproof. The thicker the PU layer, the better the waterproof fabric, equivalent to the higher mm index. However, this PU layer has a decreasing lifespan and ages over time. At higher temperatures, the PU layer ages faster.

– WATER REPELLENT: Chemical treatment technology on the upper surface (outer/right side) of the fabric, making the fabric repel/slip water (similar to lotus leaves, duck feathers, etc.), we can easily see when water gathers into beads and rolls on the fabric surface instead of sticking and wetting the fabric as usual. However, this water-repellent layer also gradually loses its effect over time and this process is faster than the PU coating, especially after each wash with soap or detergents.

4. Note about mistakes when using waterproof products:

 – One of the most common mistakes that users of Outdoor products encounter in Vietnam is when using them on motorbike trips but not paying attention to a factor that greatly changes the water pressure: SPEED.

The specific way of specifying the conditions of use for each level of waterproof index in section 2 only applies in static conditions when the tent or tent is set up in a certain place and the clothes and backpack worn on the body are used for walking purposes (Trekking, Hiking,…). However, when used on a motorbike, combined with the speed of the vehicle, the actual pressure of raindrops on the fabric increases many times, in other words, a small rain has the same effect as a heavy rain when you ride a motorbike.

Therefore, we recommend: Do not use regular Outdoor products such as waterproof windbreakers for Trekking, Trekking backpacks, Hiking raincoats, dry bags,… with limited water resistance index (with 1 mm number) for the purpose of traveling by motorbike. Instead, use specialized products such as bike racks, raincoats,… with absolute waterproof function committed by the manufacturer (Waterproof or Completely Waterproof or 100% Waterproof).

– The next mistake is soaking products with limited water resistance index. As mentioned in section 1, the time the fabric can withstand for the water pressure index it carries is limited (usually 1 minute). So it can be understood that this is the maximum level that the fabric can withstand within 1 minute. If this maximum water pressure is continuous and prolonged, then after 1 minute the possibility of water penetrating the fabric is very high.

Just like the way to use climbing shoes, it is recommended that you must continuously walk for the waterproofing ability of the shoes to be effective, but if you stand and soak your shoes in water, after a certain period of time, you will naturally feel cool. Therefore, fabrics with limited waterproofing index should not be used for soaking in water.

Hopefully through this article you will understand more about the waterproof properties of fabrics, and find the right “waterproof” product for yourself!!