MYOG – Ultralight Bivy Bag

As I was having major problems with condensation water in my one-person-tent I needed a solution that would prevent my down sleeping bag from getting completely soaked overnight. Therefore I wanted to use an ultralight water-repellent bivy bag as an additional layer between the tent and the sleeping bag.

While doing some research on the web, I found that commercial products are very expensive. For example, the Cumulus Shield Bivi, provided exactly what I needed but 90€ is really overpriced for a piece of fabric with the only task to be water-repellent. That’s why I came up with the idea to make my own bivy bag from scratch. This is not only much cheaper but also a lot of fun!

This post includes a step-by-step tutorial on how to make an ultralight bivy bag that only weighs 150g!

Bivy Bag on Scale

Choosing the right fabric

Choosing the right fabric for your bivy bag is crucial and probably the most difficult task. Your choice will largely depend your usage scenario and the conditions in which you want to use the bivy bag.

In general, you can choose between two different types of fabric. One type is entirely waterproof fabrics which protect you from outside water but suffer from low breathability. Then there are highly-breathable fabrics which are water-resistant up to a certain level but provide excellent breathability. Depending on your usage scenario (and your sewing abilities) you can either use only one type or combine them.

To keep this article in a reasonable scope I will focus on the two most popular fabrics Tyvek and Gore-Tex.

Tyvek

Tyvek is a lightweight fabric that is used for a variety of different things: it can be used as housewrap, for packaging, to sew outdoor equipment, … Because of the flexibility it is widely used in the DIY community.

Tyvek is not the same as Tyvek – there exist many different types. Generally, you can distinguish between hard-structure and soft-structure, whereby hard-structure is more resistant to water and more durable. In return, it’s heavier and noisier than soft-structure Tyvek.

Find out more about Tyvek at http://www.extremtextil.de/tipps/tyvek.html (German only).
Different hydrostatic heads of Tyvek are listed here: http://outdoors.stackexchange.com/questions/7137/how-resistant-to-water-is-tyvek-in-practice

Gore-Tex

Gore-Tex is a water-proof fabric that you probably already know from clothes or shoes. It has excellent breathability. You will have a hard time finding original Gore-Tex fabric but you can order it under the name “2/3-layer-laminat” at extremtextil.de. Extremtextil also lists the hydrostatic heads as well as the breathability for some of the laminats.

Tutorial For A Basic Bivy Bag

This is a step-by-step tutorial for a very basic bivy bag. You can use any fabric you like, I personally used Tyvek 1443R as it was the best for my use-case. Check out the links at the very bottom for more ideas or more sophisticated patterns.

Sewing Pattern

Click here to download the sewing pattern: Bivy-Bag-Pattern.pdf

Step 1 – Buy the material

Buy the right amount of material for your bivy bag. Take into account that you need probably a bit more than you expect. I bought 5m in length (1.5m width).

Step 2 – Prepare the material

Depending on the material you have to do some preparations before you can actually sew it. Especially hard-structure Tyvek should be prepared by putting it in the washing machine at a low temperature or wash it by hand. Be aware that this first washing will shrink the Tyvek  a bit.

Step 3 – Set up the fabric and draw the pattern

Fold the fabric in the middle so that it is double where you will draw your pattern. The edge where you folded the fabric will later be the very bottom. The upper edge of the fabric will later be where the “entrance” of the bivy bag is and has to line up with the opening of your sleeping bag. Do this for the lower section of the bivy bag first and repeat this procedure for the head section afterwards.

Fixate the fabric roughly with a few needles in the outer area. Once everything is setup, you can draw the pattern onto the fabric. Be sure to take your own measures into account and to make it big enough.

Important: do not draw the lines until the top edge but stop instead around 40-50cm before, like the sewing pattern suggests. This ensures that you can flip the top layer so you can comfortably crawl in and out of bivy bag. It also makes a zipper unnecessary which would be heavier and more difficult to sew.

After drawing the pattern, fixate the fabric again, but this time with more needles and much closer to the actual pattern.

Taking measurements and drawing the pattern onto the fabric
Taking measurements

Step 4 – Pre-cut the fabric

Roughly cut the material around your drawing lines (and around the needles) so that you can sew it more easily.

Roughly cutting the fabric before sewing
Pre-cutting the fabric before sewing

Step 5 – Sewing

Now you can finally start sewing. To achieve optimal results with Tyvek use the following settings on your sewing machine:

  • Thin needle
  • Sew with quite a wide distance
  • Straight stitch

Keep in mind not to sew to the top edge like explained in chapter 3.

Sewing

Step 6 – Fine-tuning

After you’ve repeated this procedure for both the head-section and the lower-section of the bivy bag, you can fine-cut around the stitches and turn the fabric inside-out. You can fix mistakes and small holes with tape.

Fine-cutting the bivy bag

Step 7 – Make a pack bag

Be creative and make your own pack bag – you can use leftover fabric from the bivy bag.

That’s it, you’ve just made your own bivy bag. Have fun with it! Please share any recommendations or suggestions in the comments below.

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Resources On The Web

These are ideas and patterns that I found useful during my research.

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