Everything in the HighLite`s design is intended to reduce weight and promote compressibility. First, the .9 ounce ExtremeLite shell fabric goes without saying. No other shell fabric is this light or packed with so many threads per inch. This specialized ExtremeLite bag uses a one way #4 1/2 YKK coil zipper that is cut to half length. While the horizontal seams are sewn-thru, the vertical seams are baffled with 1 1/2` netting to allow unimpeded loft so the effect of its 850+ goose down is fully realized. Its efficient cut not only reduces bulk and weight, but reduces excess internal volume so quick heating is realized!