How to measure water resistance?
The impermeability of a material is an indicator of its resistance to rain. Impermeability is measured in millimeters (or meters) of water column. If the material withstand a higher water column, he will behave better in case of a torrential rain.
To understand the importance of this feature, we present the measurement method:
The material stretches and fits a water column of a certain height above it. The base of the column of water can be around 10 square inches.
Wait for 1 minute. If during this time is not passing any drop of water through material, means that it is impervious to the height of that column of water.
In order to say if a tent is waterproof, the outer foil impermeability must be at least 1500 mm. I mean, a piece of that material must withstand a water column of 1 meter and a half. Some models are sold as “water resistant”. Believe it or not, waterproof is not quite waterproof! The fact that he is “water resistant” do not offer any warranty that at the first rain, water will not enter inside. Such inaccurate expressions are a way to fool buyers.
Outer foil water resistance
The most important thing you have to keep in mind before buying a model is outer foil water resistance. The outer foil is the one who has to keep the rain out!
Waterproof outer foil should be at least 3000 mm. But a value which provides a very good protection is 4000 mm of water column. One small index, for example, 800 mm means that any rain gets inside. One such product is not even tagged as being waterproofed.
Floor foil water resistance
Floor foil must be a minimum of 4000 mm waterproof coating. There are products which have waterproof floor foil of 10.000 mm. This means that the material withstand a water column of 10 meters! This index guarantees that the water will not pass through floor foil in any kind of situations.
A common situation where the impermeability of the floor foils matter is when you find water underneath the tent after a heavy rain. Water doesn’t have to go inside even if a man sits on top of it. Water gathering under the floor foil can produce 2 undesirable phenomena: osmosis or mold.
Osmosis is the diffusion phenomenon of water through a semi permeable membrane. Thus, it will reach inside. This phenomenon can be prevented either by checking after every rain, if there is water underneath the tent, either using a waterproof foil to protect the base. Check Protection section.
Mold is also an unwanted phenomenon, which harm both the material and waterproof coat, in particular the polyurethane.
Coat water resistance
The material must be covered with a waterproof layer so that water does not pass through it. There are 3 types of substances that can assure the impermeability of a material.
When is new, he does its job, but quickly deteriorates due to worn-out or pressure at which the material is submitted. This is never used for floor foil. Nowadays, this type of coating is no longer used.
Polyurethane (PU) coating is something thicker as the acrylic and slightly more expensive. Usually, apply a PU layer on the inside of the foil (outer or floor foil), in order to protect the polyurethane from the action of ultraviolet (UV) radiation or abrasion. This causes the water to permeate the fabric, but it doesn’t get inside. Thus, drying becomes a long process as the whole fabric is wet and the water must evaporate from the entire volume of the fabric.
Some nylon foils have a layer of Durable Water Repellent (DWR) coating, applied to the tent surface. This causes water to slip on foil surface, preventing it to get wet. But this layer can`t resist than 1-2 years.
The advantage of a Polyurethane coating is the fact that water vapor can pass it, making a breathable material. When it rains, water vapor can no longer cross the wet material and during the rain, we must ensure the tent ventilation, possibly by opening entries.
What it does a breathable PU is its characteristic to absorb water, the polyurethane is hydrophilic.
Pay attention! Water is a very slow solvent for polyurethane. If you pack your tent when it`s wet and he has polyurethane coating, layers will paste and turn into a solid ball. Next time, when you want to use it, it`s no longer possible to open.
Poliurentan coating is slow aging. It takes years for it to deteriorate. To extend the life of this kind of tents, the manufacturers, insert titanium dioxide (TiO2) into PU layer, in order to make this layer resistant to the ultraviolet (UV) radiation.
This type of coating is suitable for most camping tents. Prices are lower than models with silicon coating.
Practically speaking, this is a double coating. The silicone layer is applied on both sides of the foil.
The difference between polyurethane coating and the silicon one is that PU remains applied only on the surface of the material. Silicone gets into the fabric. So, in reality it`s not formed a protective silicone layer, but a reinforced fiber with silicon.
This influences some mechanical properties of the material, such as tensile strength.
PU coating makes the force concentrate in the point where it acts. That area is very exposed to the risk of tearing. The material wrapped in polyurethane material it breaks easier than a simple material with no coating.
Silicon material makes its force to be distributed over multiple fibers. Silicon material resist so much better at tearing, approximately 2.2 times better than simple material. Silicon coating provides a better protection against ultraviolet radiation more than the polyurethane. Silicon coating is recommended for tents used in the desert, tropical areas or for alpine expeditions at high altitudes (over 4000 m).
Silicon foil is not getting wet, the water does not enter into the fiber, it remains only on the surface of it. This type of material is not deep watering. These foils are flick of water or dry in the Sun in a few minutes. Unlike PU, silicon is hydrophobic, not hydrophilic. This coating is not permeable to water or water vapor. In the case of these tents must be ensured the ventilation through an appropriate aeration and, often, by opening entries.
A tent with a silicon coating can be packed even humid, because it will not stick, but he will make to appear mold. Silicon coated material is not breathable.
Silicon coating is used in case of models with uses in extreme conditions, the high alpine expedition or desert. Usually, this lining the nylon with Ripstop fabric, as its qualities significantly improves and nylon foil is lighter than that of polyester.
Water resistance tents vs. waterproof tents
There are many models, which are marked “water resistant”. It is not enough. Before purchasing, you should find information about if the desired model is waterproof. The tents are waterproof only if the outer foil withstands at least 1.500 mm of water column.