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! All at only 455 g/16 ounces, total weight.