yep, i think you've confused "650 fill" with the weight of the down. 650 fill is the TYPE of down, not the quantity. 650 fill means that is takes up a larger amount of space (650 cc) for each ounce of down vs 550, and less space than 700 or 800 or whatever. So generally speaking, the higher that number is, the lighter a bag will be for the same warmth (assuming the same construction). 10 oz of 850 fill will be a lot warmer and loftier than 10 oz of 500 fill. some people actually like the 550 fill for clothing because it doesn't squash as easily (by other clothing or pack straps). Higher fill numbers are easier to compress, and are much smaller when compressed. This makes it good for sleeping bags, when you need a lot of down. Look at the size and weight of western mountaineering bags for a comparison.