I'm about to build another quilt with 8d and apex 2.5. This might be a dumb question but why taper a quilt? I'm guessing that with the footbox cinched up it will provide a tighter warmer fit, is this the reason? I know it will cut down the weight a little too but with 8d and apex 2.5 how much? I'm thinking I'm gonna do this one with no taper for a roomier fit but I wanted to see if I would be making a mistake before i started cutting fabric. My planned dimensions are 78"x54". I'm 5'11" 200 lbs. thanks.

Your dimensions should definitely give you a nice, roomy fit on the quilt.

The taper is a common feature on quilts, but not present on all. The first open ended quilt I ever really took note of was from Jacks R Better, and was a rectangle like you are planning. I can't say I have used a rectangular quilt, but I think it should work fine.

The reason the taper is common may just be part of the UL mentality. If the quilt doesn't need that extra space, why should it be there?

As for the amount of weight you would save, that depends on how aggressive the taper is. I just checked on SketchUp, and think that using those fabrics, my taper would only save about .75oz. So you are right in deciding that the difference is really not very significant.

Tapering from top to bottom makes no sense to me either. I would keep the width 54" from the top to your hands and cut the width down at a 45% angle to 44" and taper to 40" from there.

So what would this add up to?
Your 54 X 78 quilt would have a fabric weight of 12.5 ounces, where tapering it the way mentioned above would cut 1.3 ounces or almost 10% of the weight.

A strait taper from 78" to 40" would save you 1.6 ounces or 13% of the weight.

You're also talking about having a lot of dead air space to warm up.

Thanks for your replies. I'm still debating tapering or not. I'm surprised that it's that much weight savings. When you put on in percentages it changes the way you think of just a couple ounces. Thanks.

Tapering eliminates unnecessary fabric and fill. Simple. Tighter fit around the feet and lower legs will keep them warmer, assuming you close the foot and calf area some way. I also add an abrupt taper from shoulder to neck. The result is a barrel shaped quilt. Works for me on the ground and in the hammock.