The Big Agnes Three Wire Bivy Sack is squarely aimed at the Integral Designs Unishelter. Both are made of three-layer eVent fabric, and both have claimed weights of 31 ounces. The Three Wire Bivy Sack uses a two-pole design very simlar to the 26 ounce (claimed) Black Diamond Lightsabre, but is made of fully-waterproof and highly breathable eVent fabric rather than the lighter, but water resistant EPIC fabric used by Black Diamond. The two-pole design provides more head room and potentially offers increased stability and wind resistance when compared to the single-hooped Unishelter, but the Unishelter offers more ventilation options with its tunnel vent.
The debate as to which is better – eVent or EPIC continues to rage. Three-layer eVent is fully-waterproof, but heavier than the lightest EPIC fabrics. In the fabrics used in currently available bivy sacks, EPIC is more air permeable, but has a lower moisture vapor transmission rate (MVTR) than eVent. EPIC’s breathability can suffer at temperatures just below freezing. Which is better depends on the intended use – for shower protection at above freezing temperatures, or deep winter use, an EPIC bivy will save you weight; an eVent one (properly designed and seam-sealed) will provide greater protection against sustained rain and condensation in sub-freezing conditions.
Three Wire Bivy Sack Features
- Trail Weight of 31 oz
- eVent top fabric – fully seam taped
- Nylon ripstop bottom fabric (presumably with a waterproof coating)
- Mesh bug netting closure
- Peaked visor and zipper flap over head opening
- Available June, 2007
- MSRP $299