For extreme winter conditions, take your Exped Arctic Goose WB Down Sleeping Bag with you. The Arctic Goose WB features 750-fill down to hold in your body heat and Exped's patented welded baffle construction so this sleeping bag's shell is waterproof. Welded construction means Exped didn't stitch baffles but instead glued them so the fabric has no tiny stitch holes where moisture can sneak in. A storm flap prevents moisture from getting in through the full-length zipper, and a huge hood and oversized draft collar conserves warmth. An inner pocket gives you a spot to tuck your headlamp. The Arctic Goose is rated to negative 15 degrees Fahrenheit.
Bottom Line: Take the extremely warm Exped Arctic Goose WB Sleeping Bag on your next mountaineering adventure or winter expedition.
I live in Washington and hike and climb a fair amount. I used this bag for a few outings and it is terrible. It looks nice and has good loft, but for some reason, it is just not that warm. My 0 deg Marmot was so much warmer. Actually, my +15 deg Marmot Helium EQ is warmer too I believe. This is definitely not a -15 deg bag. Trust me. It is big, bulky, weighs a lot, and is soooooo expensive for what it is. On a related note, one of my friends also has an Exped down bag that is different, but his experience has been identical. He uses it as a couch blanket.