This flexible duct has thermal insulation to prevent condensation in Heat Recovery Systems or where there is a temperature differential, for example where warm air is extracted through a cold void. It will retain heat when taking warm air to a heat recovery system and back to the rooms when the heat exchanger is in a cold void such as the loft. Maximum air velocity 30 m/sec. Maximum pressure 2,500 Pa. Available in diameters of 102, 127, 152, 203 and 254mm from stock Supplied in 10m lengths which can be cut on-site.