This year I built a bivy bag out of Tyvek 1443R. Since many people of the MYOG community are wondering how the 1443R performs, I wanted to share my experiences after sleeping in my bivi bag for a couple of nights. I used the bivi bag both as a stand-alone solution as well as in combination with my single-person tent.
According to extremtextil.de, Tyvek 1443R has a hydrostatic head of 750mm which makes it water-repellent but not waterproof. The fabric itself is really easy to handle. You don’t need any special needles or threads. I could tear the material with my own hands but I don’t think you tear it easily by accident.
Of course the material is not waterproof, so it cannot be used stand-alone on rainy days. Apart from that, the material is also not really windproof. I once had a windy night in the mountains and I have to say it wasn’t too pleasant. I didn’t feel like the temperature inside the bivy bag was much higher than outside.
On the upper hand, the material is extremely breathable. I never had any problems with condensation water at all. It’s also better to have at least an ultralight bivi bag around your sleeping bag as a second layer of shielding. It successfully kept snails away from my sleeping bag and made sure that wet grass didn’t weep my down sleeping bag. A wet bivi bag is still easier to handle than a wet sleeping bag.
In combination with a tent
The main use case for me was to use the 1443R Tyvek as a water-repellent layer inside a tent to keep condensation water away from my sleeping bag. I used it in combination with a one-person Vaude Bivi Tent.
Generally, I was satisfied in how the material performed. Some condensation water made it through the material overnight but this was negligible for me. Before I had the bivy bag, my sleeping bag was pretty much soaked and the bivy bag successfully prevented that from happening. I found that the bivy bag dried extremely quickly compared to my down sleeping bag.
All in all, Tyvek 1443R is very useful as a second layer around your sleeping bag. It’s extremely lightweight, water-repellent, highly breathable, easy to handle and still quite cheap.
It useful as a second-layer around your sleeping bag when used stand-alone to keep away dirt and small amounts of water. It’s the almost perfect material to keep away condensation water from your sleeping bag when used in combination with a tent.
However, you cannot use Tyvek 1443R for a stand-alone waterproof bivy bag. It provides almost zero isolation from low temperatures and is not tearproof enough in the long run. It is simply not built for that task.