Basically, in the item's description it mentions that it only offsets minimum comfort temp by 3C.
However, when equipped, on the character info screen (click on the minimum temp stat for breakdown) it actually offsets by double that amount - so, 6C.
I also checked out an Elkhide Duster I'd made, it also provides double the usual offset.
Finally, it's not just Elkhide - it seems that a Muffalo Parka will grant a mahoosive -90C offset.
You may want to bear these bugs in mind when playing a Frozen Wasteland challenge. No cheating! ;)
I think the problem is that the base material (as defined in Races_Animals) is supposed to give an additive offset of 1-2 degrees in either direction (I could be wrong here) but instead of being additive, the effect is multiplied.
The bug isn't the multipliers, it's the items' stats not showing it that's the bug.
It would be nice to have better information about those stat when crafting (plus have the good one showing up), it's gonna be even more important with A9 where there's gonna be a quality level.
Thanks for reporting. I'll fix this.