I'm thinking there has to have been operator error somewhere because I've had success with mine in WAY worse conditions during my AT hike this Spring and I only had a 30 degree bag. Heck....I've had my IX UQ down to 40. I will also admit to being cold on a few occasions but after checking things out carefully it was always a result of an improper hang.
Just a thought....did you shake it out prior to installing it? They say it helps redistribute the down which may have shifted when stuffing it in the stuff sack. You hold it by the sides and shake like like a bed sheet.
Someone mentioned your clothes. I've made the mistake of wearing too many clothes which resulted in becoming chilled to due sweating.
My gut feeling is that it just wasn't snugged properly....either too loose (probably) or too tight. In any event you should EASILY be able to stay warm in the 39 -40 degree range.
You can easily reach outside the hammock while laying in it and check for snugness at the head end and reach under you to check for excessive airspace. I even reverse myself to check both ends.
Keep playing with paying attention to detail.
Last edited by Miguel; 10-22-2012 at 11:24..