A microporous insulation material mixture is blended and the blended mixture is spread across a lower conveyor belt which is trained over rollers. To aid the spreading of the mixture a spreading device is used. The mixture is delivered by the conveyor to a pressing system which in this case comprises an upper conveyor belt. The pressing system also comprises a nipping means provided in this case by a plurality of upper and lower nipping rollers. The gaps between the individual rollers are adjustable. An upper fleece liner is led from a delivery roller to lie between the upper conveyor belt and the insulation mixture and a lower fleece liner is fed from a delivery roller to lie between the insulation mixture and the lower conveyor belt. The fleece liners may be used to encase the core prior to enclosing in an envelope and applying a vacuum.