For my first winter I stuffed a plastic bottle of cold water in my pack and by the second run it was a solid cylinder I could not drink from. I resigned myself to overpriced lodge soda until an older skier at a loop near the resort pulled a battered steel flask from his jacket and poured me a scalding cup of brick tea. That cup was the warmest, most welcome thing I had tasted all season, and it started a habit I will not ski without, because it solved a problem I had not even named.
Why hot tea beats cold water here
At altitude and in deep cold your body loses fluid faster than you feel, and drinking something hot encourages you to actually sip instead of neglecting hydration until you crash on the last run. A steel vacuum flask keeps tea drinkable for six or seven hours even at minus twenty, while a plastic bottle becomes a brick you have to melt. The salt and slight fat in traditional Xinjiang milk tea also replace what you sweat out, which plain water does not, and that is the part most visiting skiers miss until they cramp.
What I fill it with
I rotate between plain green tea, a strong black brick tea, and the milky salty version you get at a Uyghur breakfast stall. I pre-heat the flask with boiling water, dump it, then fill with fresh tea so it stays hotter longer and the first sip is not a lukewarm compromise. A 500-milliliter flask is enough for a resort day; for a touring day I carry a liter and treat it as emergency warmth as much as hydration, because a hot drink in a stuck situation is morale as much as medicine.
Carrying it without freezing the cap
I keep the flask in an inside chest pocket, not the pack, so my body heat helps and I can reach it on a chair without stopping and unloading. One winter I left it in an outside pocket and the cap froze shut; now I keep a warm layer philosophy for anything I need mid-day, and the flask rides inside where it belongs, next to the snacks and the spare glove.
Honest trade-offs
A full steel flask is heavy and it bangs against your ribs if the pocket is loose, so I use a slim model and a snug pocket and have stopped noticing it by the second run. Tea is also a mild diuretic, so I balance it with plain water at meals and do not pretend it replaces all fluids. And on a warm spring day a hot drink is the last thing you want, so I switch to room-temperature water when the thermometer climbs above freezing and the snow turns heavy.
Closing thought
Hydration is the unglamorous skill that keeps you skiing strong into the afternoon, and a flask of tea makes it easy instead of a chore. Borrow the local habit, pre-heat the bottle, and your future cold-self will thank you on every slow lift where the wind tries to steal the warmth back.