The ALUPROFI EXTRA aluminium loft ladder has a 46 mm thick sealed hatch. The heat transfer coefficient of the hatch is 0.85 W/m2*K. The aluminium structure of the loft ladder ensures low weight and durability for years. To increase safety, the ALUPROFI EXTRA loft ladder has been equipped with a handrail to facilitate entry and with non-slip feet. Ud - coefficient of the hatch centre.