Why do running jackets leak?

Ever wondered why running jackets leak?

  • November 4, 2021
  • Running
  • Christophe

Last weekend I ran a half-marathon in very heavy rain. Normally I’d just run in a vest and shorts (obviously shoes too!) but as the weather was REALLY bad, and I wasn’t planning on pushing it, I decided to run in my OMM kamleika waterproof running jacket. Pretty soon I was wet – or rather soaked to the skin. I took the jacket off half-way around and tied it around my waist but it was astonishingly heavy, more like a wet towel. Ironically I very rarely actually use the jacket for running so I was surprised. Very surprised. Luckily, my friend – and someone who is very knowledgeable on this subject – Mark Buskwood was on hand to help me understand why this was the case. If you’ve also ever wondered why your expensive waterproof running jacket isn’t waterproof anymore, the answer might just be here:

A little info about waterproof jackets for running and why they sometimes appear to leak:

(1) All waterproofs have a DWR (durable water repellent) applied to the outer fabric. This is what makes rain ‘bead’ into droplets. Modern environmentally friendly DWR’s are not as durable as previous versions. Once the DWR wears off rain will soak into the fabric (rather than ‘bead’ on the surface) and the fabric will no longer ‘breathe’ (so you get very sweaty). DWR wears off quickly (especially on a lightweight running jacket) if you wear a race-vest or rucsac. Confusingly, if you wear the same jacket in dry, cold conditions it will still ‘breathe’ normally. To refresh DWR use https://www.nikwax.com/en-gb/products/tx-direct-spray-on/

(2) Jacket design (in my opinion) is just as important as brand/material. Look for a hood which adjusts effectively (and ideally one that can be folded away in windy conditions if not being used), good length (I find lots of running jackets too short) and velcro cuff closures if possible, although these seem to be out of fashion currently

(3) A running jacket will always be a compromise…the ultralight jacket that is supremely breathable, totally weatherproof, durable, cheap and packs down to the size of a tennis ball doesn’t (yet) exist. Nowadays different types of waterproof shells are available for runners (see photo). I use a super-light 2.5 layer jacket with taped seams (the yellow one) for Spring/Summer/Autumn races and a more substantial 3-layer shell (the grey one) for winter/mountain use. The orange jacket is a heavyweight 3-layer Goretex mountain shell for comparison

(4) Breathable/waterproof fabrics usually have either a waterproof COATING applied to the inside of the fabric (like paint on a wall) or a waterproof MEMBRANE (like wallpaper) such as Goretex or Pertex Shield Plus. In my experience membranes are more breathable and more durable

(5) 3-layer fabrics (such as classic Goretex or Gore Active) have the waterproof/breathable membrane sandwiched between two protective layers of fabric and are best for breathability and durability…but can be heavier, bulkier and more expensive than jackets made from 2-layers (where a membrane is bonded to the inside of the fabric) or 2.5-layers (a 2-layer fabric with a texturized print applied to protect the membrane). The best of the traditional Goretex fabrics for runners (most breathable) is Gore Active

(6) Gore (Goretex) also have an interesting (and expensive) technology called ‘Shakedry’ which is used by several brands (including Ron Hill, Salomon & Haglofs). Essentially the Gore PTFE membrane (the waterproof/breathable bit) is bonded to the outside of the fabric. The big benefit is that PTFE is inherently water resistant, so the jacket should ‘bead’ rain for ever and breathability will never diminish. Whether the PTFE outer layer will be durable long-term if you wear a race vest remains to be seen…the Salomon version is designed to be worn OVER a race vest, presumably because they share this concern…pity it has a rubbish hood!

(7) Finally, don’t forget Alpkit, who tend to offer similar designs and fabrics to some of the bigger brands (Rab, Montane, Inov8 etc) but at more competitive prices. Always worth popping over to Hathersage for a look in their shop. Some more detailed info on fabrics here… https://rab.equipment/uk/guides/waterproof-jackets

– Mark Buskwood, November ’21


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