Rating: 3 / 5
15th July 2011
Terra Nova Moonlite Bivy Bag Trial
I slept in the bivy bag over night
Temperature was mild at 10deg Celsius.
I slept directly on a grassy area that was already wet and rain soaked with no ground sheet.
There were showers on and off all night.
Was in a Western Mountaineering Ultralight sleeping bag, -7deg Celsius, regular size. with a thin closed cell foam sleeping pad, torso length (shoulder to hip) inside the bivy bag.
Had a very small tarp over my head and shoulder area to keep the rain off my face.
I was wearing a light merino wool thermal underwear long sleeve top and full length light merino wool thermal long johns (wearing this only to keep the bag clean as I do not like using a bag liner)
I am 178cm tall, medium build
The bivy bag was only just large enough for my length and of a volume large enough to not compromise the insulation of my sleeping bag by compressing it when fully done up.
To sit up in the bag comfortably I needed to release the draw string hood.
It has a very long draw string with a strong and effective cord lock which does not slip even when pulled tight around your head.
Due to the length of the draw string it allows very easy access in and out of the bag. The hood can even lay completely flat which extends the length of the bag allowing you to lie on your stomach propped up on your elbows and read a book without the need of a ground sheet.
As an experiment I filled the bag with air and closing off the hood end attempted to compress it and found it to be air tight.
The Bivy Bag is very light and when packed compresses to a very small volume.
Upon examination in the morning I found the following:
There was NO water/moisture inside the bivy bag along the full length of the bottom, sides and hood area.
There was however significant amounts of water/moisture on the inside of the bivy bag along the top from approximately my hip region to my feet. The foot box area was quite wet.
It appears from first trials that the bag may well indeed be waterproof as after laying all night on sodden grass and the constant showers throughout the night the floor of the bivy was completely free of moisture. The sleeping bag being a -7deg Celsius rated bag being used at a nighttime temperature of only +10deg Celsius coupled with the extra insulation from the wool thermals i was wearing may well have created an excess of vapour the bag was incapable of dealing with. Noting also the bag was covered in water and precipitation from the rain throughout the night, possibly blocking much of it ability to release the build up of vapour within the bag.
After drying out both the bivy bag and the sleeping bag today I will again tonight trial the bag not wearing any thermals and see if that makes a noticeable difference as well as keeping both the bivy bag and the sleeping bag loose around my head and neck area. Conditions are for cast to be similar to last night. I will also be trailing the use of vapour barrier sleeping bag liner following this which will provide conclusive evidence as to if the water found inside the bivy bag is in fact the accumulation from body vapour in excess of what the bag is capable of releasing or is in fact a failure of the waterproofness of the bivy bag.
I am hoping that this bag will indeed be as waterproof and breathable as so claimed. Due to it size and weight it has the potential to be a fantastic piece of gear to incorporate into my sleep system. If it is i will be able to replace my older style gortex bivy bag which is just fantastic except for it weight at 850g and its large packable volume.