A little over a year ago I bought a light quilt (in backpack speak: a top bag without a hood) on sale from Backpackinglight. At 11 oz it was certainly light, but it wasn’t warm below 50 degrees without a jacket of some kind. Besides that we have 20 and 5 degree Western Mountaineering down bags. This arrangement doesn’t work for normal three-season temps around here when M and I go backpacking together. Things needed to change.

I also thought that a warmer synthetic bag would be handy for wet shoulder season trips. I thought about making a two-person bag, but both M and I are restless side-sleepers, and for comfort the bag would have to be so big that the warmth gained and weight saved would be negligible. I could make a whole new quilt, but Pertex ripstop is 15 bucks a yard. So I ordered 2 yards of 5 oz Climashied XP.

Ripped open the footbox and one side panel.

Sewed in a triangle of uncoated ripstop to seal things up on the bottom.
Turned the bag inside out and stuck in the new insulation.
Then sewed the sucker back up. I added periodic light bartacks to hold the new insulation in place. I may need to add some more around the feet, but the XP has a stiff hand and seems to sit in place well of its own accord.
Puffy.
Now I’ve got a 21 oz synthetic bag that with the proper head gear should be good into the upper teens.