Coolness, ventilation, fit and sweat control are the most critical comfort needs. Air flow over the head determines coolness, and larger front vents provide better air flow.
Most current BMX helmets have adequate cooling for most riders. Sweat control can require either a brow pad or a separate sweatband. A comfortable fit with no pressure points helps to ensure both comfort and the correct position of the head in the event of a crash. Weight is not a major consideration with today's BMX Helmets.