Dynamic insulation is a very good example of a ventilation system integrated with the building envelope. The paper describes two recent studies carried out at Nottingham on dynamic insulation. One study concerns a system based on mechanical ventilation. The other describes a purely natural system. Although there are few existing applications of dynamic insulation, it is argued that there is potential for both systems, particularly with certain types of building. The natural system is technically more challenging than the mechanical system, but the potential energy savings are larger. Dynamic insulation with mechanical ventilation has been investigated for an agricultural building (a pig-fattening house). The investigation has taken the form of experimental measurements in a quarter-scale model in a laboratory, coupled with CFD calculations for both the scale model and the full-scale building. The dynamic insulation is formed from lightweight re-cycled cellulose material. Measurements carried out include permeance and temperatures and velocities in the building. The system based on natural ventilation has been studied with a theoretical envelope-flow model, supported by experimental tests on components of the system. The required flow direction through the insulation material is maintained by the novel use of a wind-powered fan, combined with a passive chimney stack. At low wind speeds, buoyancy gives the required flow direction. At high wind speeds the wind-powered extract fan comes into operation. The system is completely self-regulating i.e. the higher the wind speed, the higher is the extract rate, which leads to increased pressure drop inside the building and thus the flow direction is maintained. The potential energy savings with this system are large.