User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-3150696-20110716081949/@comment-1011548-20110721125921

The MGS crossover isn't canon, you know. We can just conveniently ignore that.

The official ecology translations have a pretty good description of how Barioth's frost sac works. Basically, there's a fluid that combines with the cold air, and is mixed with it, creating the funnel shape.