How hot are full face helmets, and can I do climbs in one?

Full face helmets are significantly hotter than open-face helmets due to the chin bar restricting airflow. On sustained climbs in warm weather, most riders find them uncomfortably hot, and goggles will likely fog. Many riders remove their full face helmet for climbs and carry it or attach it to their pack. Convertible models solve this by allowing chin bar removal for climbs. If you regularly ride long climbs followed by descents, a convertible model or carrying your helmet on climbs is the practical solution. For bike park use with lift access, the heat is less of an issue since you're not pedaling uphill.