Why 130% overfill?

[warbonnetguy]

More specifically, fill power states how much volume an oz of down lofts to in a certain size and shape container while a certain sized weight is placed on top of it. It doesn't have anything to do with how much should be used in the filling process. You'd never want to use say one ounce of down per 850 cubic inches of quilt volume, that is nowhere near enough. I dont think any MFG uses those numbers to determine fill amount. FWIW, one ounce of 850FP down takes up alot more than 850 cu. inches...that 850 rating is when it is partially compressed by the weight.

Down density (how tightly the down is packed in) is as important as the amount used or the baffle height. Generally you want to pack enough in there so that you aren;'t always dealing with dead spots from alot of down shifting. If it's filled well it wont shift that much and if it does shift it wont leave a dead spot in it's place.

[Secondmouse]

You take the fill power, which is how many cubic inches of down a given fp should fill, then calculate the volume of your quilt/sleeping bag. Add overstuff if desired.

mmm, I'm not so sure it's as simple as that. I saw a formula once but can't remember where...

[Secondmouse]

More specifically, fill power states how much volume an oz of down lofts to in a certain size and shape container while a certain sized weight is placed on top of it. It doesn't have anything to do with how much should be used in the filling process. You'd never want to use say one ounce of down per 850 cubic inches of quilt volume, that is nowhere near enough. I dont think any MFG uses those numbers to determine fill amount. FWIW, one ounce of 850FP down takes up alot more than 850 cu. inches...that 850 rating is when it is partially compressed by the weight.

Down density (how tightly the down is packed in) is as important as the amount used or the baffle height. Generally you want to pack enough in there so that you aren;'t always dealing with dead spots from alot of down shifting. If it's filled well it wont shift that much and if it does shift it wont leave a dead spot in it's place.

yeah, I remember a discussion some years ago on the appropriate density and the formula to compute that but I disremember where...