Internal Wall Insulation When insulation is added from the inside, the wall must still “breathe” to avoid moisture and mold problems. Breathable and moisture-regulating materials ensure a healthy indoor climate, while vapor barriers help keep dampness away from the wall. REPLACEMENT NEEDED Possible Materials Bamboo Cellulose Cork Cotton Flax Grass Hemp Husk Mycelium Reed Sea Grass Sheep Wool Straw Wood Fibre