Going high? Headed into extremely cold regions? Go with the G1 which gives you warmth and climbing performance plus the flexibility to choose the type of gaiter you use while you are working your way from camp to camp and up the mountain. The G1 is a technical double boot, hand crafted from water proof breathable 2.8 mm split leather - for the same great fit and light weight as your single mountaineering boots. Under the leather, a breathable Sympatex membrane is sandwiched between 6mm of micro-porous EVA foam insulation and an inner cordura face. Underfoot, twin layers of 2mm Neoprene (perforated for breathability and shock absorption) plus 10 mm of EVA foam insulation back the extra-rigid technical performance midsole. Connecting you to the earth or any crampon is Boreal's MOUNT FDS-3 outsole with triple density co-molded rubber for the right combination of traction, shock absorption and durability.
The G1's inner boot is slip lasted (just like rock shoes) with waterproof split leather on collar and tongue, a padded Achilles with adjustable velcro-elastic strap (for heel retention) plus a unique raised heel that keys into a corresponding cavity in the floor of the outer boot. Materials include a durable Cordura outer, W/B Sympatex, Thinsulate for warmth and an efficient wicking Dry Line inner surface.
The G1excels at technical mountain routes and high altitude expedition style climbing. Wear yours for extremely cold mountaineering in New England, the Rockies and all peaks up to 7,000 M.

Sizing: If a US 10.5 fits well in a hiking boot, then order a UK 10 for a similar fit.