The word cellulose comes from the French word for a living cellule and glucose, which is sugar. Insulation is low-thermal-conductivity material used to separate the internal climate and sounds of a building from external climate and sounds. Cellulose insulation is plant fiber used in wall and roof cavities to separate the inside and outside of the building thermally and acoustically.
Cellulose is the oldest building insulation material. Many types of cellulosic materials have been used, including newspaper, cardboard, cotton, straw, sawdust, hemp and corncob. Monticello was insulated with a form of cellulose. Modern cellulose insulation, made with recycled newspaper using grinding and dust removing machines and adding a fire retardant, began in the 1950s and came into general use in the US during the 1970s.
The market for insulation increased following the oil embargo of 1973-74. The embargo caused energy costs for heating to skyrocket across the nation, which lead to increased interest in energy conservation measures. Insulation gained significant national attention as a cheap and available technology to increase the energy efficiency of homes. In 1977, following a particularly severe winter, a tax credit was given for homeowners who installed insulation.
While in 1976 there were roughly 100 cellulose insulation firms with 125 plants, by 1978 there were more than 350 firms with more than 500 plants1. Cellulose insulation was produced locally by small manufacturers who purchased ready-to-operate machines and offered a cheap and easy low-tech production process. Other than some constraints created by a shortage of boric acid for use as fire retardant, cellulose captured an increased share of the market due to lower costs and its suitability for retrofits. Meanwhile fiberglass and rockwool producers found it difficult to keep up with the demand for insulation from their customers.
Due to complaints by retailers, contractors and consumers about price, safety and quality control problems, the federal government began enacting insulation standards beginning in 1978. There was a great concern that the growth in cellulose manufactures was leading to improperly or insufficiently treating insulation against the threat of fire even though reliable statistics on a national basis did not exist. This led to the Federal Consumer Products Safety Commission passing 16 CFR Part 1209, which sets safety standards covering four product attributes for cellulose insulation only: settled density, corrosiveness, critical radiant flux and smoldering combustion. Another regulation passed was the “R-value Rule,” placing clear limitations on the claims that manufacturing and marketing firms can make about their product.
The effect of regulations by the CPSC put most of the small producers of cellulose insulation out of business. The costs incurred by increasing fire testing made cellulose more expensive and the bad publicity helped decrease demand. They were either unable to meet the testing requirements or they merged with other small manufacturers. In 1985 the CPSC asked Congress to repeal the flammability standard after further studies. By 1991 only 61 cellulose producers still remained in the US. 
The fiberglass industry meanwhile benefited from most of the regulations passed by the federal government. The heavy lobbying by the more centralized fiberglass and mineral insulation manufacturers helped pass the tough fire standards for cellulose insulation. These standards were reinforced by technical bulletins published by the Mineral Insulation Manufacturers Association (currently known as the North American Insulation Manufacturers Association) that promoted fire hazard claims against cellulose insulation. These claims were not independently verified, faced little scientific review, and were misleading and untrue.
Currently cellulose insulation has increased again in use in the United States. Part of the reason for this growth are studies that have shown results that suggest that cellulose may actually protect a building from damage in a fire better than fiberglass because cellulose is denser than fiberglass and doesn't allow the oxygen necessary to burn structural members. Several National Research Council Canada studies
 have backed these claims. Another major reason for the comeback of cellulose might be because of the increased interest in green building. Cellulose has the highest recycled content of any insulation material and also has less embodied energy than fiberglass and other furnace produced mineral insulations.
Four major types of loose-fill cellulose products have been developed under a variety of brand names. These are generally characterized as dry cellulose, spray applied cellulose, stabilized cellulose and low dust cellulose. These types are used in different parts of a building and for different reasons.
Dry cellulose is used in retrofitting old homes by blowing the cellulose into holes drilled into the tops of the walls. It can also be blown into a new wall construction by using temporary retainers that are clamped in place then removed once the cellulose has reached the appropriate density. This form of application does settle as much as 20% but the stated R-value of the cellulose is accurate after settling occurs.
Spray applied cellulose is used for applying cellulose to new wall construction. The only difference could be that water is added to the cellulose while sprayed in avoiding the need for a temporary retainer. The insulation might also have a percentage of adhesive mixed in. This form of applying insulation usually gets rid of settling problems but needs to dry for up to 48 hours before being covered.
Stabilized cellulose is used most often in roof insulation. It is applied with a very small amount of water to activate an adhesive of some kind. This reduces settling and decreases the amount of cellulose needed. This can prove advantageous at reducing the overall weight of the product on the ceiling drywall helping prevent possible sag.
The last major type of cellulose insulation on the market is low dust variety. Nuisance levels of dust are created during application of most types of dry insulation causing the need for simple dust masks to be worn. This kind of cellulose has a small percentage of oil or similar dust dampener added. This may also be appropriate to homes were people are sensitive to newsprint or paper dust.
The thermal performance of loose filled cellulose compares favorably to other types of insulation. The R-value (insulation) for loose-fill cellulose is approximately 3.8 per inch. The r-value for loose-fill fiberglass is approximately 3.2 per inch. This doesn’t represent the whole picture of thermal performance. Other important aspects are how well the building envelope is sealed from air infiltration, convective airflows, and thermal bridging.
Cellulose is very good at fitting around items in walls like pipes and wiring leaving few air pockets that can reduce the overall efficiency of the wall. It also seals walls from air infiltration while providing the density to limit convection. The University of Colorado School of Architecture and Planning did a study that compared two seemingly identical test structures, one with cellulose and the other with fiberglass. The cellulose structure had used 26.4% less energy to heat. It also was shown to tighten the structure more than 30%. Subsequent real world surveys have cellulose performing 20-30% better at reducing energy used for heating than fiberglass.
Compared to foam insulation, cellulose has a lower R-value per inch, but is much less expensive; its R-value per cost is much higher than foam.
Noise reduction is achieved in three ways with cellulose. The first is that cellulose completely fills cavities leaving few air pockets for sound to travel in. The second is the cellulose materials ability to trap air. The significant difference between noise reduction with cellulose and fiberglass is its density. Cellulose is approximately three times denser then fiberglass. This helps deaden the sound through walls and between floor levels.
Cellulose is 75-85% recycled paper fiber, usually post-consumer waste newsprint. The other 15% is fire retardant such as boric acid or ammonium sulphate. Cellulose has the highest recycled content of any insulation available. Fiberglass has a maximum amount of 30% recycled content by example.
Embodied Energy and Emissions
The embodied energy of cellulose compared to all other insulation is by far the lowest. It requires 20 to 40 times as much energy to produce furnace-made insulation materials compared to cellulose. Cellulose is made by electrically powered machines while mineral insulation is made in furnaces. Cellulose is also made with locally available materials other than the fire retardant, while mineral insulation factories have to ship materials and products over greater distances.
Unlike foam insulations, many of which use HFC or HCFC blowing agents which have global warming potential hundred or thousands of times higher than that of carbon dioxide, cellulose does not produce significant gaseous emissions.
Insulation is Green
All insulation helps make buildings more energy efficient. Using cellulose insulation can contribute to obtaining LEED credits in the US Green Building Council certification program. It can earn credit in two categories: the energy and atmosphere energy performance category and the materials and resources recycled content category.
Cellulose insulation can be very dusty during insulation and it is recommended that a standard dust mask be worn while working. The fire retardant Boric Acid is about as dangerous as table salt. There is slight concern over the off gassing of ink from the newspapers but the material is sealed behind walls, and no studies have shown this as an issue.
McGrath, Ed (1981). The Super Insulated House; A working guide for owner-builders, architects, carpenters and contractors. Fairbanks: That New Publishing Company.
Home Insulation: Hearings before the Subcommittee on oversight and investigations of the committee on interstate and foreign commerce; House of Representatives Ninety-fifth Congress; Second Session; February 21, 22, and 23, 1978
Serial No. 95-81
Enforcement of a cellulose insulation safety standard; Hearings before the Subcommittee on oversight and investigations and the Subcommittee on Consumer Protection and Finance of the committee on interstate and foreign commerce; House of Representatives Ninety-fifth Congress; Second Session; April 19, 1978; Serial No. 95-100