Cellulose Insulation
Cellulose insulation is made from recycled newspaper or wood fiber treated with borate fire retardants. It is dense, non-toxic, and has the lowest embodied carbon of any common insulation. R-value is about R-3.5 to R-3.8 per inch. Cellulose is installed two ways: loose-fill (blown into attics) and dense-pack (blown into wall cavities at ~3.5 lb/cu ft). Dense-packed cellulose is one of the highest-performance cavity insulations available — it conforms around wires and pipes, slows air movement, and stays put for decades.