So I'm looking to cut gear weight as much as possible and one means I'm thinking of is a packable, hooded, down coat for the upper half of a sleeping bag. I'm always tossing and turning and the darn bag twist with me, also trying to zip it up and down as needed is a pain. I was thinking that I could bring the coat for the upper and cut a sleeping bag in half and use a draw string for the bottom. Is this doable and worth a try?

Try a quilt.

My husband uses that exact sleep system and loves it. Feathered Friends (Seattle) will custom make an "elephant's foot" (half bag) for you. His is 800 down and weighs nearly nothing. He uses a North Face expedition parka. Also have to have good gloves.

What you're talking about has been done. An elephant's foot bag is what you're looking for.

http://www.backcountrygear.com/brooks-range-elephant-foot.html?gclid=CK_wjqWEgr0CFYtDMgodYXwAoA

Or a quilt. Quilts are nice.

I'm thinking the half bag would be better because the coat serves double duty but then again a quilt would be a little extra warmth without to much extra weight. Couple ounces at most. Now its quilt vs half bag! I saw 2 military half bags on ebay last night but they weigh in close to 2lbs. Hmmmmmm

You are going to have to pay quite a bit to get a high quality low weight half bag. The high quality down is expensive whether in a quilt or half bag or jacket. You are paying for the reduced weight.

Why couldn't I buy an older down sleeping bag and cut and sew that into a half bag?

First, "old" down bags were made before the new 800-900 down was available. Depends on the old bag - if it is a 650 down (the most common type of bag in the old days) it will be heavy; an elephant's foot made of an old bag will also be heavier than what you could buy now.

Have you ever sewn with down? Very touchy and feathers everywhere! First, you need to have more than "half" the bag to make an elephant's foot. You need the bag to come at least to your waist when finished. For most people, legs plus body to waist is more than half their body length. Second you need to leave about 2-3 inches minimum to finish the seam and put in a drawstring. Because of the feather problem you need to cut the bag above a horizontal seam. This may result in more than waist height.

One trick if sewing with down, wash the bag first and then handle it when the down is partially dry so feathers do not fly everywhere. You have to be careful because if the down is too wet it is heavy and will rip out the internal baffles.

However, if you just want to try it to see if you like the system before investing in an expensive elephant's foot, it may be a good experiment. But do not expect to have a light half bag.

One of the steps in instructions on how to make down gear is usually to isolate yourself - in a tent, a bathroom, a closet, or some other easily cleaned, confined area - to maneuver down into the baffles.

Then there are other instructions involving using a shop vac with a clean pair of pantyhose over the business end, to move down around.

I suspect opening a baffle of a down bag in an unconfined space will resemble something like having a flock of exploding geese fly into your house.

Observe the many ways backpackers have dealt with this issue.
http://www.backpackinglight.com/cgi-bin/...thread_id=33573

I was checking that out, that's an interesting way to do it for sure, Be almost worth looking for damaged 800+ down coats n bags on ebay to make my own. Unless there's a good place to buy down fairly reasonable. I'm short, 5'2" so it shouldn't be too heavy when its all done. I'd like to incorporate some snaps or something that attaches it directly to the coat.

I was recently in a head on collison (and I'm fine, modern car technology is amazing). As a result I was picked up by an ambulance crew from the side of the road wearing the always-in-my-truck-in-the-winter 800 FP down parka. While they strapped me to the board, immobilized me, and cut every piece of clothing from me with their shears - they did take *off* my parka.

Talking to the medic who rode in with me apparently it's kind of a rite of passage for new guys to screw up once and cut a down parka off someone in an ambulance - the result is an impressive mess