My weight doubles, but my volume more than doubles.
The reasons? ....
Obviously layers of warm clothing.
Switch from alcohol stove to inverted canister stove.
Heavier, bulkier sleeping bag/quilt.
More sleeping pad insulation.
More food. (warming energy).
Got to positively stay dry - rain pants, dry bags.
Water crossing shoes (crocs).
Snowshoes/crampons(love my Kahtoola Microspikes).
Then there is the intangible component. Since winter is not forgiving, I tend to err on the side of caution when packing, which I'm sure adds more than few ounces.