The present invention provides a calcium sulphate-based product (e.g. a wall board) comprising gypsum and silicone oil. The product may be produced by drying an aqueous slurry comprising calcined gypsum and the silicone oil. The silicone oil is included in the slurry in an amount greater than 10 wt % which results in a product have greater than 8.5 wt % silicone oil. This improves structural integrity of the wallboard after exposure to elevated temperatures.