The Evolution and Chemistry of the Waterproof Jacket
- Emily
- Feb 4, 2022
- 6 min read
Updated: Feb 5, 2022
If you live in the UK, like me, you’ll have tried your fair share of waterproof jackets to protect you from whatever the weather throws at you.
When I was younger calling a coat “waterproof” seemed an overstatement; they either didn’t keep me dry, or it felt like I was wearing a bin bag. With the existence of leading waterproofing technologies such as GORE-TEX, eVent, and Futurelight, waterproof is just one of many high-tech properties in the latest jackets. But how does the modern technology in our coats work?
The Mackintosh
The waterproofing of clothing can date as far back as the Aztecs in the 13th century, where natural latex was combined with fabric. However, the first (commercially made) waterproof jacket was invented by the Scottish chemist Charles Macintosh and Thomas Hancock’s clothing company in 1824. Macintosh’s waterproof design came from finding uses for waste products from chemical refinery in the gasworks. He discovered that rubber could be dissolved in coal-tar naphtha, a gasworks waste product, which was then used to waterproof fabrics. His patented design, which was later used for the Mackintosh Coat, involved the sandwiching of this liquid rubber between two pieces of fabric. These waterproof jackets were heavy, smelly, and uncomfortable to wear. Problems arose when stitching the coats made holes in the fabric and varying temperature affected the stiffness/stickiness of the rubber. The latter was improved when vulcanized rubber, heat cured rubber that can resist temperature changes, was introduced in 1839. The advances in waterproofing technology, however, occurred after the development of polymer chemistry and water-repellent coatings in the late 19th century.
Nowadays waterproof jackets are breathable, stretchy, and incredibly light thanks to improvements in materials technology. Waterproof fabrics are separated into two main groups: hydrophobic (water repelling) microporous membranes and hydrophilic (water loving) non-porous support layers. Modern waterproof jackets often involve the use of polytetrafluoroethylene (PTFE), a hydrophobic, microporous membrane sandwiched between densely woven/non-woven fabrics. The power of the expanded PTFE (ePTFE) membrane was first patented by Bill Gore (founder of brand GORE-TEX) in 1970 after he discovered that by expanding the incredibly strong PTFE membrane, it exhibited low water absorption properties.
“What you gain by making [a waterproof jacket] air permeable is a lot more comfort.” – Martin Hatfield (eVent fabrics)
For a fabric to be breathable it must allow water vapour from your body to diffuse through the fabric and enable evaporative cooling (sweat evaporating from skin). The PTFE membrane in these waterproof jackets has 14 million/mm2 micropores which are small enough to stop liquid water (rain) from passing through but large enough to allow water vapour (from sweat) to escape, making them simultaneously breathable and waterproof. Since Gore’s development of GORE-TEX jackets, other brands; eVent, Futurelight, and Neoshell, have adopted similar techniques for their waterproof fabrics and garments.
GORE-TEX Technology
The original GORE-TEX material started to leak over time due to the body oils (from sweat and sun cream etc.) inhibiting the pores of the ePTFE from blocking out water. So, despite this material being extremely breathable it gradually lost its waterproof ability. This led to the introduction of coating and laminating of the ePTFE layer to protect from these body oils. The side of the membrane that is in contact with the fabric support layer, that touches the skin, is often coated in a hydrophilic polymeric solution, such as polyurethane (PU). The PU soaks up the sweat and makes the fabric tougher. Due to the thickness of the PU coating the breathability decreases; however, this technique is still used on jackets as it is cheaper. A hydrophobic polymer, such as polyvinylidene fluoride (PVDF), is often used to coat the outer layer of the jackets to prevent water saturation and encourage beading. This PVDF coated layer showed loss of its water durability over time, becoming heavy when saturated in water. The UK’s first GORE-TEX waterproof jacket was made in 1977 for Berghaus. While both the PU and PVDF coatings promote waterproofing, they reduce the effects of breathability - making them less comfortable to wear. This is where eVent and GORE-TEX fabrics become different. eVent replaced the PU layer with an oleophobic layer (oil-resisting) to protect the membrane from body oils. Martin Hatfield, from eVent fabrics, said: “what you gain from making [a waterproof jacket] air permeable is a lot more comfort”. GORE-TEX, however, removed the PVDF layer so that the ePTFE membrane was on the outside of the jacket. GORE-TEX realised that by removing this outer layer, it not only increased the breathability but made the fabric more light weight. The durability of the ePTFE layer was increased by introducing an oil-resistant fluoropolymer, commercially known as Durable Water Repellant (DWR).
The Laminate Structure
Laminate waterproof jackets are the most effective (and most expensive), where the waterproof membrane is bonded to the other layers. There are three main categories for these laminate jackets: 2-, 2.5-, and 3-layer shells. 2-layer shells comprise of the face fabric coated in DWR on top of the waterproof membrane, 2.5-layer shells have an additional protective print (half layer), and 3-layer shells have a backer fabric. The price of the jackets increases as you increase the number of layers in the laminate. 2-layer shells are the cheapest, they often have an additional lining sewn to the shell for comfort – increasing the weight of the jacket and decreasing the breathability. The protective print in the 2.5-layer shells helps to protect the waterproof membrane and add comfort. 3-layer shells are the most expensive but have a better performance. Backer fabrics act as protection for the waterproof membrane and is more comfortable against the skin. Face fabrics have the greatest impact on the weight of the jacket, and its desired uses. A soft, flexible face fabric would be used in a jacket for fast moving activities, whereas a tough face would be used in activities requiring a bit of protection.
Another waterproofing technique is the NikWax Analogy, used in Paramo jackets, which eliminates the use of a waterproof membrane. These jackets consist of two layers: a DWR treated polyester face fabric and a ‘pump liner’. The pump liner uses wicking (capillary action) to remove moisture from the body. The advantage of these jackets is that they not only remove water vapour but they remove liquid sweat too. While these jackets have their advantages, they tend to be heavier than the ones previously stated.
DWR and Contact Angles
DWR is a superhydrophobic coating that is used with ePTFE to prevent it from becoming water saturated and losing its breathability. This is the component that is responsible for the water beading you see when you wear a high-tech waterproof jacket in the rain. The DWR is superhydrophobic, it has a high contact angle. The contact angle θ, depicted in the below image, is the angle at which a liquid interface meets a solid surface. A higher contact angle means the water droplet has less contact with the surface. In this case, when the rainwater touches the DWR covered jacket, it gets repelled, and it forms a droplet/bead. Owing to the small amount of contact the water droplet has with the jacket, the micropores in the ePTFE are only partially covered by water meaning the jacket is still breathable. This water beading can just be shaken off the jacket. The most common DWR is a long chain C8 fluorocarbon, but this has many environmental problems linked to it: toxicity and persistence in the environment. Greenpeace found worrying traces of this fluorocarbon in high altitude lakes around the world, highlighting the impact this chemical coating is having on the environment. There are efforts to make a more sustainable DWR coating. Patagonia, among many others, have begun researching other alternatives to this C8 fluorocarbon. From 2016, Patagonia started using a C6 fluorocarbon as a temporary fix until they find a fluorocarbon-free solution.
The hydrostatic head (HH) of a waterproof jacket can tell you how much water pressure it can withstand before water is let in; the higher the HH value the more it can endure. The measurement derives from the height of a column of water required to make water leak through. Jackets’ HHs vary drastically based on the quality of the membrane and DWR. GORE-TEX and eVent, the leading waterproof brands, typically achieve HH values of up to 30,000 mm. This HH will decrease with wear as the DWR degrades and becomes less effective over time. The contact angle becomes lower, saturation is increased, so the jacket becomes less breathable. Factory applied DWR can be restored by washing and tumble drying the jacket, where the heat from the tumble dryer reactivates the waterproofing. Washing your coat with special waterproofing treatments (such as NikWax treatment) can restore and retreat the DWR treatment, increasing the breathability of the jacket.
The evolution of the waterproof jacket has come a long way from the 1824 Mackintosh, thanks to advances in polymer chemistry. The trade-off between comfort and performance has become less of an issue as both are now achievable with the latest technologies. The problem now faced by these companies is the sustainability and environmental impact of their garments, but with company promises and sustainability goals like Patagonia’s hopefully these can be conquered soon.
Written by Emily Cuffin-Munday
Blog References:
Alpkit (2021) [https://alpkit.com/blogs/spotlight/how-waterproof-jackets-work]
A. Mukhopadhyay, V. K. Midha, Journal of Industrial Textiles [https://doi.org/10.1177/1528083707082164]
A. R. Tehrani-Bagha, Advances in Colloid and Interface Science [https://doi.org/10.1016/j.cis.2019.03.006]
B. Halford, Chemical & Engineering News [https://cen.acs.org/business/consumer-products/raincoats-evolved-keep-us-dry/96/i16]
M. Mattone, S. Rescic, F. Fratini, R. Manganelli Del Fà, International Journal of Architectural Heritage [https://doi.org/10.1080/15583058.2017.1290850]
Comments