IMPREGNATION and LAMINATES
You might not have been interested in this article in March and April 2020 because hardly a drop of rain fell from the sky and being soaking wet was difficult to imagine. That’s why we waited until today to show you all the intricacies of water resistance and waterproofness of our materials and how to attain them.
Let’s start from scratch.
WATER RESISTANT or WATERPROOF?
What does water resistance mean? Contrary to what it may seem, words which are shown as synonyms in a dictionary have a completely different meaning for sportsmen and tourists. The outdoor equipment and clothing industry, or if you prefer the outdoor recreation sector, offers the following division:
It means that the material does not soak immediately, but it does after a shorter or longer rainfall. The material does not lose its properties on contact with water and is resistant to water. However, this does not mean that water will not penetrate the material. The term water resistance does not guarantee total protection against soaking.
Water resistance is mainly influenced by the density of the fabric, which increases proportionally to the weight of the fabric. We can assume that the heavier the fabric, the better it will cope with moisture. Imagine that during a downpour you are standing under a tree. You will get wet, but much later than if you were standing directly in pouring rain.
In addition, nylon and polyester are the two best-known water-resistant materials.
Impregnated, or water repellent means that resistance to water does not depend on the texture of the fabric or the density of the weave. It results, however, from the additional treatment of coating the material with additional protection. There is no systematic scale in this respect, which would give us clear information about what is more or less impregnated…
A term from the impregnated materials family. Hydrophobicity means the tendency of chemical particles to repel water molecules. Such material literally defends itself against moisture.
Regardless of whether the material is impregnated or hydrophobic, the coating wears out over time. It will therefore require refreshing and reapplying the substance.
WATER RESITANCE vs IMPERMEABLE
Water resistant is not impermeable. The material’s water resistance is relative and depends on the material’s resistance to water column pressure.
The value is given in mm. The higher the figure, the higher the material durability. The higher the value, the greater the chance that the garment will not get wet in a downpour.
A material is considered to be waterproof if it can withstand a minimum water column pressure of 1,000 mm per 1 m² of material. Full water resistance can be said to exceed 10,000 mm H2O. We can imagine that setting up a 10-metre tube in laboratory conditions is quite a challenge. Such measurements are currently done with the Suter Tester.
Water tightness is a term that relates e.g. to electronic devices: watches, cameras and smartphones. We don’t use it to measure the resistance of fibres to permeability.
The matter is not so simple because at first sight it is not easy to determine whether the material is covered with a water resistant or waterproof layer. We will be helped by tags and product descriptions. Each of the popular impregnants, apart from being waterproof, has a range of properties that need to be taken into account:
– impact on material strength
– impregnation durability
– resistance to mould, water and UV rays
– applicable with flame retardant coatings
Materials that are not coated with a water-resistant layer are mostly laminates, i.e. multi-layer combinations of membranes and fabrics with different properties glued hot into a single, compact whole.
WHAT TO IMPREGNATE NYLON AND POLYESTER WITH?
Resistant nylon or polyester by themselves are unable to assure ideal water resistance. Once the fabric is sewn and dyed, we apply a water repellent layer, choosing one that would be the best solution for the purpose.
The choices are as follows:
PU polyester urethane
PE polyether urethane
Mix of the above
We also swam in the ocean of impregnation possibilities, so we know that you can drown there even with a lifebuoy on.
Whatever happens, prepare to compromise. It is either going to get soaked, or it’s going to be heavy, or it’s going to be expensive :).
Let us have a look at the kinds of coatings:
Acrylic is applied on one side of the fabric. When it is completely new, its coating is water resistant and shiny. Unfortunately, it wears off quickly over time, mainly due to the friction of the material layers against each other.
For tents, friction is not an issue, but in the case of trekking trousers, it is. When in motion, the trouser legs rub against each other. In many cases, a thin coating of acrylic is used to stabilize the fabric weave rather than for impregnation. Acrylic belongs to the category of “drizzleproof” rather than waterproof impregnants.
Durable Water Repellency (DWR) is permanent impregnation of fabrics, including knitted fabrics, added during the production process in the factory. DWR technology prevents water from being absorbed by the fabric, making it condense on the surface and run off freely. This type of solution is used in the production of clothing, shoes, hammocks, or tents. Durable water repellents are commonly used in combination with waterproof and breathable fabrics, but the use of DWR can reduce breathability.
The effect of DWR is not permanent, as general use and contact with contaminants will reduce the lifespan of the coating. The symptoms are increased weight and condensation (the fabric appears to be leaking). Therefore the DWR coating should be re-applied from time to time.
You’ll find impregnation renewal preparations of companies such as Grangers, Nikwax, McNett, and Trek7. There are also chemical ways to use DWR, which is by spraying or dipping. Recently, chemical gaseous preparations have been added. This eliminates harmful solvents, reduces the use of chemicals and gives the fabric a more natural look.
All ripstop materials available in our shop have a factory-applied DWR protective coating, which can rinse out after about two years.
PU polyester urethane
PU is the most commonly used polymer, i.e. plastic. It is a liquid insulating sponge. It has become a standard in the production of outdoor equipment. PU is most commonly used because it satisfies many user requirements at a decent level. It can achieve premium water resistance of up to 10,000 mm and is additionally fire resistant. It is also inexpensive.
Unfortunately, PU application has a negative impact on material slippage. The more porous the material, the more the fibres rub against one another. PU gets into the strands and “cements” them in one place, reducing slippage. This makes it easier for the fabric to be torn apart. The difference is more or less the same as when cutting one ragged thread or five slippery threads at a time with a knife.
PU coatings are hydrophilic. This means that they like water, which they absorb on prolonged contact. The whole process is slow and depends on how long our tent is exposed to bad weather conditions. If you plan to backpack in the monsoon season in Sumatra, it would be logical to use several PU layers. However, there are issues with that, too. The more PU layers, the heavier the tent and the weaker the material.
Once soaked, PU needs a lot of time to dry out. Soaked nylon stretches and loses its elasticity. The tent’s rain flies start to hang up and stick to the walls. Not nice. Another battle is fought with mould and fungi, which adore such moist climates. Microorganisms develop quickly on a PU medium and can consume its protective properties. When PU breaks down, the chemical compounds smell really bad. If you leave your tent in the rain for a few days, you can be sure that PU will disintegrate and stop working. Make sure the tent is bone dry before you stash it in far corner of the closet.
Not only does moisture damage the protective coating but it also peels off the laminated seams.
PU offers the worst HYDROLITIC STABILITY. This means that over time PU reacts with water, even with a small amount of it from the air, and its particles start to tear. The decomposition process of PU is further accelerated by high temperatures.
By storing our tent in a dry, shady place, we can delay the disintegration but will not avoid it altogether. Once started, hydrolysis cannot be stopped, even by meticulous cleaning. You may remember the nostalgic smell of an old backpack with a frame, pulled out by your father from a basement. This is hydrolysis at its best.
These facts do not discourage tent manufacturers. A tent coated with a PU layer can easily hold for a decade ( 10 years 🙂 ), by which time we will have replaced it by a new one…
PU is an impregnant that can become waterproof. Everything depends on whether we apply it only on some of the fibres, a selected piece of the material or the whole surface.
Modern technologies help to increase breathability thanks to micropores. Steam escapes outwards through the holes while raindrops do not get inside. The material breathes, unfortunately not enough to leave the skin dry after a steep ascent with a full backpack. The PU breathability level will never be sufficient for high physical activity. Compared to basic DWR, it is heavier but more environmentally friendly.
PE polyether urethane
PE is a lesser known impregnant, less frequently produced and therefore more expensive.
It has similar properties to PE, is applied in the same way and can also be combined with flame retardant coatings.
PE is most often used for the floors of expedition tents, used in more severe weather conditions. During long expeditions into the wilderness, weight does not matter as much as the strength and permeability of the material.
PE is even less stretchable than PU and reduces the abrasion resistance of the fibres even further. Actually, it can only be used in materials whose initial strength is very high and its weakening will not affect the effectiveness of use.
PE has hydrophobic properties, i.e. it almost completely repels water. Unlike PU, PE is resistant to mould and fungi.
The impregnation is usually applied from the dry centre, so mould does not have a medium to feed on. What is important for exotic expeditions, PE is resistant to hydrolysis, even in humid, warm climates. This does not mean, however, that you do not have to take care of tarp!
Silicone is an inorganic polymer, or a high molecular weight chemical. If you associate silicone mainly with the bathroom and shower cubicle, it is very good.
Silicone is non-sticky, hydrophobic and poorly reactive. It is smart enough not to enter into chemical reactions with other substances. It doesn’t bond with anything, even water. Everything flows down it like down a duck’s back.
It is perfect for impregnating thin materials, whose fibres it strengthens.
The amount of silicone that can be used for impregnation is limited. It is not possible to apply several layers of it, so waterproofing with thin fabrics can reach only 1,500 mm. This is not of great significance since silicone itself is hydrophobic. It is easy to dry a tent or jacket by simply shaking them off well.
Silicone does not undergo hydrolysis and is resistant to mould and fungi. However, if left wet, a rolled-up tent or jacket can get damaged but will not stick.
As the only one of the three, silicone strengthens the material (even twice) acting on the fibres like a lubricant. It gives them additional slip and thus resistance to breakage. For this reason, in small quantities, it is often added to ordinary materials.
These are the indisputable advantages.
But there is also a flip side to silicone. When it is used for impregnation, we cannot well laminate the threads with a tape (e.g. at the zippers). You can stitch them with a double-eye system. Silicone cannot be combined with fireproof coatings. The biggest disadvantages are a steeper price and lack of breathability.
Outdoor recreation, adventure and nature is often inseparable from mud, rain and water. Wearing wet clothes and carrying a wet tent is the least pleasant association. That is why the manufacturers of outdoor clothing and equipment rack their brains to combine such seemingly unconnected properties as breathability, weight, durability and water resistance, often the most important feature from the point of view of the user. Since you can’t have everything in one impregnant, technology gives you the chance to combine them.
The PU silicone mixture is used on the inner side of the material. In this way PU is protected from UV rays, abrasion and excessive moisture. Rain can soak into the material and will need more time to dry. A few moments in the sun and wind and silicone will dry out completely.
In cloudy weather, the drying process will take longer. PU lets in water vapour. It breathes, enables the use of a fireproof layer and use of sealing tape on the seams.
Thanks to the presence of silicone, the material will stay dry longer than when using PU alone. On thin materials, this mix allows for increased waterproofness to 2,000 mm H2O.
Strength remains neutral because silicone strengthens and PU weakens the fibres.
It is also possible, in theory, to use each of the impregnants on either side. This is a balancing act, though, and requires a lot of experience. We remember that silicone adheres to virtually nothing. If silicone penetrates too deep into the fibres on one side, PU would not stick to it on the other side and you will be able to scrape it off easily. In such a situation, the PU side can have laminated tapes and the silicone side can be sealed with adhesive. However, applying impregnants in this way will not prevent PU hydrolysis.
In both cases, the silicone will make it easier to pack the material by affecting the slippage.
SIL/SIL means that silicone was applied on either side of the material. This gave rise to our favourite portmanteau words: SILNYLON (nylon coated with silicone) and SILPOLY (polyester coated with silicone. SIL/SIL works very well with light, delicate materials. It strengthens them and prevents abrasion. It also has a miraculous self-healing property. Small holes can “heal” by themselves.
The thickness of the material determines the amount of silicone applied. This means that thin materials will have limited impregnation possibilities. As a result, they will protect against rain but will not be waterproof. The SIL/SIL solution works well with equipment and clothes that are supposed to be very light and durable but not necessarily waterproof and breathable.
The biggest problem is to set priorities. Would I prefer to be drenched in sweat and wake up with swollen eyes due to lack of oxygen in the tent? Do I want the juicy greenery of my tarp to resemble melted mint ice cream after two summer seasons? Do I wish to carry a heavy if rotting backpack or a dry if flammable one? If this choice is too much of a burden, use the table below to set your priorities.
Instead of PU, PE, silicone and DWR, you can of course use the DIY option: drive an iron over beeswax or diligently rub a candle into your jacket. You can also rush to a Castorama store for white spirit, press a tube of silicone into it and spray the mixture over your backpack. Then you can spend the night keeping your fingers crossed for it to work. You can also choose to chemically impregnate it :).