Prepare yourself for backcountry enlightenment when you head out with the Black Diamond Revelation Avalung Winter Pack. The Avalung system uses a special breathing tube that gives avalanche victims critical breathing time when they222re buried in the snow. This mid-sized pack is ideal for long day tours or overnight hut trips thanks to its spacious interior, and a slew of ski-specific features prepare you for any backcountry contingency. The Avalung system uses a special breathing tube that gives avalanche victims critical extra breathing time when they222re buried under the snow.