Waterproof trousers: preparation

So another essential project has come up. I swear I am working on the wedding dress, but this one came with (more) time pressure and some financial pressure too.


My first pair of homemade waterproof trousers.

My other hobby when not sewing is hillwalking. Over the years this has intersected with the sewing in a few interesting ways. This is at least partly because  the RTW selection for women for technical equipment is limited – despite the blub about being fitted for women it is often designed to fit slender women with small curves. One project I made in the past was a pair of waterproof trousers. An ambitious project you say? You would be correct –  I only undertook this due to need. I tried nearly every pair on the market and couldn’t find a pair that fitted well, and certainly not a decent quality pair. Therefore I made a pair about three years ago for our big trip to New Zealand. This pair had fit and construction issues, but they also lasted about 18 months (longer than most RTW parirs). When they died I planned to make another pair – I even bought the fabric I needed. Unfortunately I ran out of time and had to buy the least badly fitting RTW pair I could find to see me through a trip.


The final fatal rips for the RTW pair – temporarily fixed with duct tape.

That was last summer – I have been putting it off since. To be honest, I don’t find this an exciting sewing project – rather a necessary one. Therefore, when I finally got two large rips in the bum of my RTW pair it was time to fulfil another one of my new years resolution – use my waterproof fabric.

You may have seen them making a ‘waterproof’ garment on the Great British Sewing Bee. They lied – that garment was NOT waterproof – although they seam sealed the shoulder seams EVERY OTHER seam on the garment would have leaked, including the collar, which seemed to be designed to funnel water down the neck as far as I could tell. And don’t get me started on the ribbing on the waist and cuffs, apparently designed to wick moisture up. Also that nylon fabric was HORRIBLE. So please forget this.

As there is less written about sewing functional technical clothing I thought I would detail more of my thought processes through two blog posts. This first one will be about my planning and fitting process.

It is important to understand that with waterproof trousers function is everything – the way it looks is virtually irrelevant (at least to me). These trousers need to withstand the Scottish weather for ten hours or more. If you have never spent time in serious rain and wind this is hard to explain, but the water forces its way into any available crack and hole. Therefore my priority has to be waterproofing. The fabric is essentially plasticised on one side, and every hole in it e.g. pin holes and needle holes, reduces its waterproofness. My second priority is longevity – firstly because I don’t want to have to make a pair of waterproof trousers frequently both due to cost (good waterproof fabric is pricey) and time, and secondly because as waterproof fabric wears its waterproofing deteriorates, therefore becoming less compatible with priority one.

202-DrawingThe basic pattern I have used for this is the women’s Korouoma pant pattern from Shelby – a fantastic online store for technical fabric and products, based in Finland . They also have a really useful range of technical patterns for purchase. The first time I made waterproof trousers I made a number of changes to this pattern:

  • The big one: My legs tend to rub together when walking and this can wear the fabric away along an inside leg seam. Therefore I decided to join the front and back leg pieces together into one huge y shaped piece to remove the inside leg seam. This sent the grainlines squiffy, but I wasn’t too worried as the plasticised nature of the fabric means the fabric does not really drape – I just estimated the grainline running straight down the piece which seems to work fine.


    The whole leg pattern piece.

  • IMG_2939

    The waterproof zip with stormflap behind.

    to fit the trousers I did my standard adjustment for trousers and shortened the thigh section by an inch

  •  another relatively easy one – I added a waterproof two-way zip up 2/3 of the way of the outside of the leg, and a storm flap behind this to catch any water that got through, and a zip garage at the top of each zip to prevent water going in the top of the zip


    the cuff reinforcement in cordura.

  •  obviously I did not use the pockets which are an option in the pattern, but I did use the cuff reinforcements in the leg which was sewn in a tougher cordura fabric (fabric chat in the following post)
  •  I also added a patch using the cordura to reinforce the bum – this was just sewn on top of the waterproof fabric using topstitching


    the bum reimforcement piece. not sure if you can see the two lines across the bum, but something tried to rip through the fabric, and was stopped by the reinforcement. – therefore proving the worth of this addition (the death of the RTW pair also shows this)

  •  finally, I decided I wanted to reinforce the knee. I can’t remember the thought/experimentation process, but I ended up with a knee patch which I was planning to sew in the cordura. However, at some point after I had cut the fabric I discovered that the cordura was not waterproof, and therefore ended up sewing the patch I had created in the waterproof fabric. In the end the patch did not fit well and ended up affecting the waterproofness of the garment.


    The problematic knee patch. Note the rubbing along the inside seam, which is why I removed the other inside leg seams.

So when I got the pattern out this time I already had those alterations in place. But I hadn’t been entirely happy with the trousers I made, so there were some alterations I made

  • I removed the unsuccessful knee patch and reinstated the darts from the original pattern. I considered taking these out altogether because it does add more stitching which adds more risk for waterproofing, but I decided to keep them as they help with the shaping of the leg for walking.
  • I extended the waistband upwards to make a highwaist. This was to get rid of my eternal problem of the jacket riding up and trousers being pushed down at the back under my rucksack. I suspect part of the problem here is that I have a long back.
  • I made a pattern adjustment for a ‘large seat’, which basically lengthens the crotch curve and adds extra fabric to the back section of the trouser, as they always felt tight here.
  • IMG_3052

    Diamond gusset piece


    The patch I added to my first pair of trousers when they split on the crotch.

    I added a diamond gusset to the crotch. A diamond gusset increases the range of movement for the trousers. There are a few reasons why I thought this would be worthwhile. Firstly it would increase the range of movement when wearing the trousers. I think this is important because my previous pair of trousers finally died when they split along the crotch seam, I think this was due to a combination of the strain put on the seam by the need for a larger seat, and the lack of flexibility within the available seams. Adding a diamond gusset is pretty easy in principle – you cut out an appropriately sized diamond and work out where the lowest part of your crotch curve is, and insert it here.

After making my pattern alterations I made a mock-up. With waterproof clothing this is ESSENTIAL, as everytime you cut into the fabric you endanger the waterproofing – you can’t risk cutting it wrong and ruining the whole project (as exemplified by my failed knee patch adjustment). I found some cheap waterproof nonbreathable nylon in my local fabric shop which acted more like the proper fabric would than any flexible draping fabric.

When playing around with my mockup I discovered a few things to fix:

  • the knee darts were higher than my knee, but the overall length was right, so I moved them down, but left the length the same
  • the waist needed to be fractionally broader to get over my hips comfortably – an easy fix
  • The height of the waistband was roughly right, but it was still dipping in the middle of my back. after checking there was no longer any pulling across the seat, I added on a wedge  to the top of the back leg sections to even it up all the way around
  • Once I had finalised the bum pattern I redrew the bum reinforcement patch, making it slightly smaller than the previous version as the lower part of the previous version was well below my bum, so this lower section was unnecessary.
  • IMG_2955

    the diamond gussest in the mockup.

    Finally I needed to put the diamond gusset in. I wasn’t sure where it needed to be on the crotch curve, so I waiting until I had the mockup on to mark the lowest part of the crotch curve, slice out the required space and pin it in place. I couldn’t believe the difference it made – with it in suddenly it was easier to move my legs in all directions – both forwards and backwards and side to side. I was so impressed I pinned the gap up again to feel the difference – without the gusset I really only felt comfortable moving my legs backwards and forwards. I will definitely think about adding a diamond gusset to other patterns to improve the available range of movement.

Wow, that is a lot of info already, and there is still so much I still want to talk about (fabric, construction techniques… I think I will leave it there – pattern pieces ready to go. To be continued….

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6 Responses to Waterproof trousers: preparation

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  6. Tori says:

    I have a quick question about the Korouoma Pants pattern. I just recently received my pattern, and have had an extremely difficult time taping the pieces together so I can trace it onto my pattern paper. The print is so faint that I’ve had to go over everything with a sharpie, and even then, the boxes don’t seem to match up; the end result would be more than a few centimeters too short.

    Did you encounter this problem? How did you manage around it?

    Thanks so much!

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