Zpacks Winter sleeping bag liner, turn a 3 season bag into a Winter bag or use it as a Summer 30 degree sleeping bag, 15 oz, 3/4 center zip.

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1) as a Winter Sleeping Bag liner, Black .75 oz/sqyd Pertex Quantum GL on the inside for quick drying, the inner material is .51 cuben and makes a Vaper Barrier. I would think this would make a 20 degree bag warm down to about 5 degrees.

2)As a 30 degree summer bag it has an outer .51 cuben which opens to a quilt so no bivy required and it handles condensation well, the inner staying dry. At about 39 degrees I needed to put on fleece socks, at 29 degrees I was warm with down booties and a jacket, at 60 degrees I just opened it as a quilt and was fine so it has a wide range. However the cuben shell doesn't breath so you need to leave the neck open or open it as quilt if it's warm out.

I'll post photo's later tomorrow.