How durrable is the elastic component of a Montbell U.L.Super Spiral Down Hugger?

Montbell has been making stretch bags for a few years. I'm not sure when they started making bags with this kind of design, though the oldest product info and reviews I can find are from 2005. My Montbell UL Super Stretch is four years old and has held up very well, with no deterioration of stretch.

IMHO, the UL Super Spiral is going to last just about as long as the UL Spiral. Not because the elastic is indestructible but because the kind of fabric used on pretty much every UL bag and quilt is inherently more delicate and abrasion adverse than the 70D nylon/polyester used on bags like the one my dad has been using on BWCA trips for the last 30 years.

Both the UL Spiral and UL Super Spiral will last you at least 10 years if cared for properly, but if a 20 year lifespan is what you're after, it may be worth looking at the heavier Montbell Super Spiral (non-UL) bags, which use a 40D nylon rather than the 12D nylon used in the UL Spiral and UL Super Spiral.

I have a "Heavy" low volume(2300) pack with great suspension, so a small compressed volume is almost as important as weight.