Insulation

See Insulation ABCs at the Healthy House Institute for an overview of some common and alternative insulations.

Avoid These Insulations: Fiberglass (both formaldehyde and formaldehyde-free versions); rock wool or mineral wool; rigid foam and cellulose.

Better Options

Sheep's wool is often thrown away during spring shearing or stored in barns to be forgotten for ages. Farmers have trouble finding a market for it, especially since the wool needs to be thoroughly cleaned before being marketable, which can be a time-consuming process without the right infrastructure.

Two companies, Oregon Shepherd (West Coast, US) and Black Mountain (East Coast, US) have managed to capitalize on this abundance of cheap wool, which happens to have very good qualities for use as an insulation. Wool has an R value of 4-per-inch and it can also absorb and breakdown indoor air pollutants such as formaldehyde, nitrogen dioxide, and sulfur dioxide.

For better or worse, Oregon Shepherd's loose fill and batts are not simply raw wool. It is treated to "enhance [the] wool's inherent fire-retardant properties" with Boric Acid 1.6% and Sodium pentaborate decahydrate 6.4%. The company also uses a proprietary formulation using a natural protein (probably Casein SL) to covalently bond the borate compound to the wool fibers (see Sheep Insulation Comes to America).

Black Mountain's wool contains 4% recycled polyester and is also treated with 4% borate. 

How harmful, if at all, is Boric acid and Sodium pentaborate decahydrate in those concentrations? I don't know. Here is a "fact sheet" on Boric acid that might be helpful: Boric acid. At very diluted concentrations, Boric acid has been used as an eye wash and for other home remedies, but then again, so has bleach and mercury. Like all medicines, it seems that dosage is the key factor. I haven't been able to find helpful information on Sodium pentaborate decahydrate, but I have seen it listed as a herbicide.

Another wool option is to track down local or regional ranches that pasture sheep and see if you can buy it direct. Stop in at the local yarn shop and talk to the people in there. If you get raw wool, it should be washed thoroughly.

Bonded Logic's Ultratouch Denim insulation. These batts are made of 85% recycled denim mixed with 10% Boric acid, Ammonium Sulfate and a "binding fiber" (5%) called polyolefin. Also contained in the insulation are the chemicals that were in the blue jeans, such as dyes and pesticides.

R value is about 3.5. Ultratouch can be found at Home Depot and other stores like it.

AirKrete is a cement-based insulation product and supposedly entirely inert and non-toxic. The primary component is magnesium oxide (MgO). Air Krete is created with the addition of a tiny bit of ceramic talc, water and a "foaming agent." Once it's ready for use, Air Krete looks like shaving cream. It is sprayed into walls, much like many modern foaming insulations, and also like them, can be quite messy to work with. In fact, Air Krete is typically installed by specialists. Once it's properly installed and dry, Air Krete shouldn't expand or shrink, unlike other spray-in-place insulations. Air Krete dries to a rigid foam, trapping its many millions of air bubbles inside.

Unfortunately, AirKrete has few installers across the country and none in California. AirKrete's insulation value is R-3.9-per-inch. See the MSDS.

Rice hulls is a very promising insulation option. Here is an overview of its properties and testing results: The Rice Hull House.

Hemp insulation is another interesting option, but it's only available in Canada and Europe. See Thermo-Hemp by Ecological Building Systems.

Perlite and Vermiculite have also been used as insulations, usually as masonry fill.

This company is in the testing phase of an insulation made from mushroom mycelium.