Traditionally, a ski boot was designed for going downhill with as much speed and power as possible, with little thought to the comfort when going uphill. With an aggressive sole material like Vibram, lightweight shell material, and the now-standard lever to switch between walk and ski modes (to free the cuff to rotate or lock it in place), the alpine touring boot changed everything. This is the boot to take into the backcountry.
An alpine touring boot is either compatible with a standard alpine ski binding (DIN normalized binding), a TECH binding, or both. There’s little difference between the boots except for the extra heel and toe fittings required for a boot to be TECH compatible.
A stiff boot will have a high flex rating (120-130+), while a softer boot will have a lower flex rating (100-110). Stiffness benefits you during the descent, but it might cause you pain on the skin track—consider whether you prefer superior comfort or performance.
A carbon cuff or tongue, lightweight plastic shell, minimalist buckle design, or honeycomb structure help reduce the weight of an AT boot so you can move faster and feel less fatigued during a long tour.