Rating: 3 / 5
My new 2007 model 800-fill bag failed bigtime in the warmth department. Even with ample layering, pad, and use inside a tent, I couldn't seem to shake off annoying cold spots and a palpable sense that my body heat was leaking through the bag like a sieve - even despite overnight temps no lower than 45F.
By way of reference, my usual 3-season bag is a Marmot Hydrogen (30F), which has proven dependable to or below its rating, and at essentially the same bag and fill weights, and fill power.
So what's going on here?
My bag went back to Montbell on a possibly-confirmed hunch of an underfilled baffle or two. MB claims their bags are QC'd for fill wt but not per baffle - and the design of the Down Hugger series incorporates many baffles. The purpose of all those baffles, of course, is to keep the down from shifting and so to reduce the overall quantity necessary to achieve x amount of warmth.
Is there a "down" side to all those baffles, though? In the case of the Super Stretch bags, my feeling now is that there is. Underfilled baffles are one thing, but the SS's myriad baffles present another concern. It isn't difficult to imagine how inefficient such a design would be were the baffles of sewn-through seam construction. And while they are not in fact sewn-through, the elasticed "super stretch" circumferential baffle seams are so taut against the bag - even when relaxed - that they actually mimic a sewn-through baffle construction.
Note the scalloped appearance of these bags, per the imagery on MB's website, and compare it to the smooth, even look of the Alpine bags with standard non-stretch seams along the exterior fabric face.
The Super Stretch bags essentially compress their insulation at the baffle seams, creating a total-bag heat sink that I believe is the primary reason for my bag's unexpected failure, moreso than the effect of any underfilled baffles.
My experiences with this bag were bad enough to warrant a 2-ish rating, but I'll add a star thanks to Montbell's top notch customer service in the aftermath. The Super Stretch concept is smart, in theory if not by my experiences in actual practice. And for sure, the stretch design is also tried-and-true by MB's longstanding claims. My gut sense tells me that it may work better in some (thicker) applications than in others.