I first heard about British army bivvy bags through Al Humphrey’s excellent blog post about microadventures and bivvying. He’s a fan of the army issue bivvies and I was acting on the advice in his article when I bought my first one online.
Unfortunately, the bag I received was old (1994) and in a pretty bad state. It was also “Grade 1”, which means that it’s only had one owner and is meant to be in pretty decent nick. The first time I used it, a lot of water got in at the base, the surface material was “wetting out” (becoming saturated with water), and to top it off there was a nice hole in the head section. However…
I could see how, if it were functional and undamaged, it would be a fantastic piece of kit. So I didn’t want to give up. I found a local army surplus retailer, visited the store and got myself another one. This time it had a DPM camo surface (not olive green), there were no holes and it was issued in 2010…so not quite 25 years old like the last one.
And it’s one of the best pieces of kit I’ve ever bought. I love it. It’s (more or less) watertight, very breathable and nice and roomy.
If you’re thinking about buying an army bivi bag, read this little guide first. If you buy online, it’s often luck of the draw. But you can make sure you get a quality product if you take a few precautions.
Having the right expectations with waterproofness
There’s a video on youtube of a kid standing in a reservoir with an army bivvy. They are very waterproof, but they’re not impermeable (no breathable fabric really is). So it’s important to remember that when you’re using it without protection in very heavy rainfall/on damp ground that water can get it (though it should be very minimal).
A friend of mine in the army said that the main use of bivvies is to stop your sleeping bag from getting damp and protect from dew. This is why they’re almost always combined with a tarp and sleeping mats, especially in inclement weather. The army issue roll mats are 10 cm longer and 10 cm wider than typical store-bought mats to account for the whole of the sleeping bag/bivvy.
So you want to avoid keeping it out in lots of heavy rain and having the base in contact with sodden ground, where water can leech through. I don’t have an oversized mat and I’ve found that it’s very easy for my feet to end up resting on the wet, cold floor. You can read about army roll mats here. They’re available new from the company that makes them for the military (unlike bivvies).
The condensation issue
The big issue with bivvies is condensation. Over the course of the night you will release lots of moisture in the form of perspiration. The “dew point” is the temperature below which this water will condense and form droplets. Because the outside of your bivi is in contact with the cold outside air, droplets will condense on the inside surface. The idea with breathable bivvies is that a large amount of this water vapour can pass through the permeable fabric (Gore-Tex) without condensing.
The army bivvies perform brilliantly in this regard. I think the size and vapour-permeable material combine to make something that seems almost impervious to condensation. I’m yet to try it in really humid conditions, but it certainly performs well in the cold. I assume the larger size improves ventilation (where air carries moisture out of the bag).
The problem with humidity is that for vapour transfer to occur (from inside your bag to outside) it needs to be less humid on the outside. Humid air dissipates. So if it’s a very humid night, don’t be surprised if condensation starts to form.
DWP and Gore-Tex deterioration
I’m no fabrics expert and if anybody wants to jump in and correct me please leave a comment. Over time,the durable water repellency (DWR) of your bivvy will diminish. A DWR isn’t responsible for waterproofness (that is achieved by the Gore-Tex membrane). Rather, it is a water repellent finish that is applied to the outside fabric of the bag that causes water to bead and roll off.
With army bivvies there are a few problems relating to waterproofness, breathability and general wear and tear. First off, as already mentioned, the durable water repellent (DWP), with which the surface fabric is treated, degrades with time. This results in what’s called “wetting out”, where the outer fabric becomes saturated with water. You can overcome this by cleaning and reproofing (described below).
If your Gore-Tex membrane is relatively in-tact, there shouldn’t be any issues with leaking. However, it’s when the Gore-Tex membrane deteriorates that you start to run into trouble. Because the bivvies experience a lot of wear, micro-cuts (invisible to the eye) can occur in the Gore-Tex, making it more permeable to water. Imagine piercing the fabric of your bivi with a fine needle dozens of times. That’s going to make it less resistant to water. If you think about all the wear a bivvy has had (forest floors with stones, thorns, pine needles etc.), then you can see why age can be an issue. You want a bag that’s as new as possible.
What to look for
Here’s my checklist for buying:
- Make sure you can read the printed text in the head area. This is a good indicator of wear as well as age. Go for an issue year as close to now as possible. Keep in mind, however, that some bivvies don’t have this printed text.
- The seam tape should not have been replaced (replaced tape often looks dark brown).
What you want instead is tape that looks almost transparent, the same colour as the inner liner (more or less).
- No obvious signs of wear and tear and the like. Holes are a big no no.
- Drawstring attached! I’ve no idea why people remove them.
Looking after your bivvy
Generally, looking after you bivvy means keeping it clean and reproofing it every so often (once a year or every two years, depending on how much you use it).
Nikwax “Tech Wash” is designed specially for cleaning Gore-Tex materials. Detergent can block pores further so avoid it if possible. “Nikwax Wash-In” is probably the easiest way of reproofing as it goes straight in the washing machine.
Where to buy?
Go to a shop and check the age, quality and general wear and tear. You should be able to see the year and other printed text (it shouldn’t be worn down as in the picture abovr).
I understand that not everyone has a local army surplus store, and one of the best options for price is eBay. Click here to have a look. Just make sure you ask all the right questions!
What are your thoughts? Leave a comment below!
What are your thoughts and experiences? Please leave a comment below and let me know!