Waterproofing is a measurement of amount of water pressure that a fabric can take before water passes through the fabric. The millimeter (mm) rating represents the measurement of water pressure. This measurement can tell you how much water pressure a jacket can take, as well as if a jacket is the right one for specific weather condition.
How tall of a column of water sit on top of the fabric measures the water pressure for a fabric. If the column of water is short, the pressure of the water on the fabric wont push the water through the gaps in the fabric. However, if the column of water is too tall, the weight of the water will create a powerful water pressure that push the water through the fabric.
How Waterproof Ratings Work for Jackets and Tents
The wind also creates water pressure when it blows against a jacket, as well as when the person moves their body while wearing the jacket. Therefore, a jacket with a low water pressure rating may fail if the weather contain alot of water and wind. Light rain contains less water pressure then heavy rain, so a jacket with a lower water pressure rating is sufficient for someone who is going for a casual walk.
However, if there is a steady shower, the water pressure on the jacket with a low water pressure rating may lead to the jacket becoming soak. For individuals who are going to be hiking or skiing, a heavy downpour is likely to occur, so they will need a jacket with a higher water pressure rating to allow the fabric to take the heavy water pressure. While the fabric from which a jacket is made is important in determining how well it will remain waterproof, the seam on a jacket can also allow water to enter the garment.
The seams on a jacket may have many small hole in them due to the way that they are sewn together with only needle and thread. To prevent water from entering through these seams, people often tape jackets. Some jackets may have seam taping on only the area that are subjected to the most stress on the garment.
For jackets that are designed to experience heavy rains or storms, the seams on the garment should of be taped on all seam. If there is insufficient seam taping on a jacket, water will enter the garment through these seams even if the fabric of the jacket has a high waterproofing rating. Durable Water Repellency, or DWR, is a chemical that a person applies to the outer fabric of a jacket.
DWR isnt the same as the waterproof membrane use in the jacket. However, DWR acts as the first line of defense against water entering the jacket. If the DWR break down, the outer fabric will absorb water from the environment.
The saturated fabric will prevent the waterproof membrane from allowing the wearer’s sweat to escape the jacket. If the sweat cannot escape the jacket, the wearer will feel clammy and cold within their garment. You can reactivate the DWR treatment by placing the garment in a dryer on a low heat setting, as well as by using a spray on treatment on the outer fabric of the garment.
Maintaining the DWR ensures that the waterproof membrane continue to be able to breathe. Breathability is another characteristic of a waterproof jacket other than waterproofing. Breathability is the ability of the fabric of a jacket to allow moisture vapor to escape the jacket.
The more breathable the fabric of a jacket is, the more difficult it will be for a person to sweat while wearing the jacket. As a result of the waterproofing and breathability trade-off, it is possible for a person to become wet in there own sweat while wearing a highly waterproof jacket. To counteract this, one can use a layering system for their clothing.
A breathable outer layer can be worn with a base layer that will wick moisture away from the body to manage the humidity within the clothing. The rules of water pressure can be applied to camping gear, such as tent. A tents rainfly does not require a high water pressure rating because the angle of the rainfly will naturaly allow water to bead off the fabric of the rainfly.
However, the floor of the tent do require a higher water pressure rating than the rainfly. This is due to the body weight of the sleeping camper creating a high amount of water pressure on the tent floor, which can cause water from the ground to enter the tent floor.
