Convesa 150 VENTILATED FIRESTOP WHITE T.W. MULTIFUELStainless steel AISI 316L in the inner wall and AISI 304 in the outer wall. Rock wool: density 180 kg m3, thickness 25 mm. Total absence of thermal bridge. For natural draught boilers (negative pressure) and forced draught (positive pressure up to 200 Pa with seal) which work in dry or wet conditions (condensation) and use gas, gas oil or solids (firewood, coal, pellets, etc.) as fuel.