I would have purchased a different type of bag liner, but received the Montbell warm-up sheet as a gift.
Having used it, I like it. The draw string on the warm sheet allows one to draw it tight around the neck for extra warmth. Used it with the Montbell Super Stretch #3 Down Bag. Together them kept me warm to 28.
This review was written in the old system and had content requirements that are different than reviews written today.