The best way to rehydrate food in these conditions is to follow the pan method on the packet. In extreme cold, it avoids the problem of pouches freezing before they are fully rehydrated.
Can I use your meals in minus conditions or at high altitudes?
We intentionally set out to design a range of meals that could be rehydrated and eaten straight from the pouch wherever you are in the world, just by adding boiling water. However, rehydration does take longer at higher altitudes, and heat cools faster than normal in sub-zero conditions.

