How does this jacket compare in warmth to the MontBell ultralight down jacket? Is it a little heavier and warmer? I need something that will stand up to detroit winters under an outer shell.

I believe this jacket is in between the MontBell UL Tec Down and UL Down Inner for warmth. I tried on all 3 tonight, and am leaning towards this jacket. I am looking for an insulation layer, and feel the UL Down Inner is a bit too light with fewer features. The UL Tec Down has similar features but seemed more of an outer layer than an insulation layer. This jacket seemed to fit the job of insulation layer better than those 2. Also, I am a Small in this jacket but a Medium in the MontBells, if that helps answer size questions.

Both of those jackets have the same exact fill power. The shell on the Montbell is 15d Ballistic Airlight nylon with DWR coating. So it may be a bit more water resistant by itself w/o an outershell. The MontBell is also warmer due to the outer shell.The Zeus also has a DWR coating (check marmot.com for detail). I would say the zeus is warmer than the mb ultralight. Both have same fill power and similar shells but the avg weight of the ul is 7 oz vs 14 oz for the zeus. Even if the shell/zips/etc are 2-4 oz more on the zeus, I am guessing the additional weight difference is the amt of fill being used...which for the mb ul is about 2 oz (montbell site).