Glass mineral wool is rot-proof, odourless, non-hygroscopic, does not sustain vermin and will not encourage the growth of fungi, mould or bacteria. It is made from sand, recycled glass, limestone and soda ash. These are the same ingredients that are used to make familiar glass objects such as window panes or glass bottles. The glass is spun to form millions of fine strands of wool and a resin is used to bind the wool together to form a mat of material.