I have a ~0F "very warm" bag that does not have a "cinch" draft collar. I cinch down the chin and hood, but when I move around I can still suck a little cold air into the bag (and I assume it constantly lets a little warm air out throughout the night).

I know nothing replaces a good draft collar, but any thoughts on a lightweight option (e.g. down vest) that I could use to block the draft from occuring? If I lay a fleece blanket across my chest it does the trick, just need a lighter weight option. Thanks!

You could roll up a towel into a tube and use that as a make-shift draft collar. If not a towel then another shirt or similar.

Are you handy at sewing? I have a custom-order Feathered Friends bag with a removable draft collar, which is basically a down-filled snake that slides into a collar sleeve with snap closure. If you can add the sleeve you could use about anything for the insulation.

Cheers,

My first thought is that the bag (unless you have slept in it already at those temps) maybe not as good quality as you think...draft collar/hood is pretty standard on any mummy type bag.

My son sleeps with a throw fleece, which is about 1/3 + smaller than the average fleece blanket or liner. At anything lower than 20 F or so we both sleep w a loose balaclava hood.

Any piece of fleece clothing probably is the most sensible as you are already bringing it along, weight and size wise.

My wife wraps a light synthetic shirt around her neck and says it solves the problem perfectly. And it's light, and multipurpose, in that she sometimes wears the shirt as well...

Which reminds me I sometimes carry a fleece "neck gaiter" that is basically a turtleneck without the pesky shirt. Weighs 1 ounce.

Unless you already are wearing all your clothing in the bag, just use any piece of clothing. I have a 4 oz. down sweater that I wrap around my neck. You could also simply sew a drawstring sleeve on the inner fabric of the bag for a draft collar. The draft is due to air circulation, not lack of insulation. All you need is something to block air flow.