This is one of my personal favourites. Not only it has the lowest K-value (0.035), its eco credentials are high and shiny. Considering the amount of paper that is consumed by the media industry, the world would be a better place if we managed to recycle a tiny amount of it. The only reservation I have about it, is the grey energy that goes into producing this material – approximately 35kWh per cubic meter. This energy is needed to strip the material of all chemicals and nasties and soak it with mineral salts to make it fire-proof. However, the non-eco materials (like mineral wool) can consume around 100kWh of grey energy per cubic metre. When you have recouped its grey energy, the mineral wool has settled and shrunk and you need to replace it. So, forget about the grey energy of recycled newspapers – it helps keeping the trees where they should be – in the forest.