Are other materials better than blown mineral-wool fibre?
There are two other materials commonly used for cavity wall insulation – foam and bonded polystyrene beads. If properly installed, these materials should theoretically be superior to mineral-wool fibre, as they are inherently waterproof. Neither material is used as widely as mineral-wool fibre because of cost. It can take two or three days to inject a house with either of these materials, and the cost is likely to be several hundred pounds, so they are not favoured by the government-funded schemes (which budget on around 100 per house for mineral-wool fibre). Neither material is without its problems, however. Bonded polystyrene bead insulation has been reported to transmit rainwater across cavities. Although the individual polystyrene beads themselves are waterproof, if the cavity filling is incomplete, it can leave voids which are able to fill with water, and depending on the configuration of the voids, these can channel water across the cavity, instead of dripping straight down as ad
