A Brief History of Thermal Insulation

From caves to superinsulated houses, human beings have demon­strated the need for protection from the elements. The true origins of the science of thermal insulation, however, are difficult to iden­tify. Organic materials have served as the natural prototype for thermal insulators. Evolutionary examples include fur covering the polar bear or feathers on a bird, cotton, wool, straw, and even hair. Similarly, prehistoric human beings clothed themselves with wool and skins from animals and built homes of wood, stone, earth, and other materials for protection from the cold winter and the heat of summer.

For thousands of years, house structures were designed to best suit the climate of their location. For example, using the earth as an insulator, the Egyptians retired to the coolness of subterranean chambers and grottoes on hot days.1 Historians believe that the ancient Greeks and Romans discovered asbestos and found many uses for it because of its resistance to heat and fire. The Romans even used cork for insulation in shoes in order to keep their feet warm. Pliny, in the first century, referred to the use of cork as an insulating material for roofs. Early inhabitants of Spain lined their stone houses with cork bark, and North African natives used cork mixed with clay for the walls of their dwellings.2

As technology developed, so did innovations to improve the com­fort of human beings. Introduction of the fireplace and chimney by the Norwegians and people of Iceland during the twelfth and thir­teenth centuries provided controlled, artificial heat.1 It was evident

that the task soon became not only how to keep heat out but also how to keep heat in. The thatched huts of northern Europe were built with a roof, up to 2 ft thick, of woven straw and walls of clay and straw (Fig. 1.1) Early Spanish mission houses of the south­western United States, where temps rose to 120 to 140°F, were comparatively cool due to clay straw walls several feet thick. Similarly, the indigenous peoples of the South Seas built huts of dried sea grass. The hollow fiber of the dried sea grass provided a good degree of thermal resistance.2 Mineral fiber—another impor­tant insulating material—was first used by the natives of the Hawaiian Islands to blanket their huts. The fibers came from vol­canic deposits, where escaping steam had broken the molten lava into fluffy fibers.

It was not until the advent of the industrial revolution of the late nineteenth century that deliberate commercial application of ther­mal insulations became mainstream. For example, blanket-type insulations were being developed throughout the 1890s. One such product, known as Cabot’s Quilt, was introduced by Samuel Cabot in 1891. The material consisted of a matting of Zostera marina, a marine plant also known as eel grass, sandwiched or stitched between two layers of kraft paper. (An unrefined use of this mate­rial was found in the Pierce house of Dorchester, Massachusetts, built in 1635, with Zostera marina stuffed between the framing members.)2

Mineral wool was first commercially produced as a pipe insulator in Wales in 1840 and in the United States for the first time in 1875.3 It was almost 60 years later, in 1897, that С. C. Hall, a chem­ical engineer, produced rock wool. By 1901, he was producing this product commercially at a plant in Alexandria, Indiana.2 Hall formed a partnership to make the new product and later founded Banner Rock Products Co. (which was purchased by Johns Manville Co. in 1929). By 1928, there were eight plants manufac­turing either rock wool or slag wool insulation in the United States. (By the 1950s, this number had increased to approximately 90 but has since declined to about 15 to 20 today.4)

Fiberglass had its first beginnings in ancient Egypt, when people discovered that they could draw hot glass into threads, which were placed around vessels for decoration. The modern technique of making fiberglass insulation, developed in 1931, involves jetting of molten glass through tiny heated holes into high-speed air streams, wherein the resulting fibers are drawn very thin and to great length.5 Developed by Owens-Illinois, the Corning Glass

Company was the sole producer of this material, later known as Owens-Corning fiberglass, until an antitrust action filed in 1949 by the Department of Justice.4

Wood shavings were a very popular insulation product due to the wide availability of raw materials and their low cost at the turn of the century. Shavings often were treated with lime or some other chemicals to increase resistance to water absorption, fire, and fun­gal growth. These were called balsa wool or balsa batt (actually sawdust wrapped in paper) and were popular in homes of north­eastern United States.

Straw bale construction also has been around since the “frontier days” of the United States and is most common in the western Plains states. When the Kincaid Act of 1904 opened part of Nebraska to homesteading, straw was one of the only indigenous materials available. Housing became an urgent necessity for fron­tiersmen, and straw bale construction flourished in the Sandhills of Nebraska more than any other known location. Although these settlers planned to build a “real” house as soon as enough money could be saved, such houses often were left exposed on the outside, but they were plastered on the inside to enhance tidiness and pre­vent drafts. Although the process sometimes took as long as 10 years, the outside walls would finally get a thick coat of mud plas­ter or cement stucco.

Straw bale construction was an appropriate, sometimes neces­sary response to a unique combination of legislative, geologic, nat­ural resource, and socioeconomic factors that prevailed in that region. The building of railroads through the Midwest is one factor that added to the reduction of straw use. Railroads and merchan­dizing enabled wood products to replace Nebraska’s indigenous materials for buildings needs.

Reflective insulation materials, using bright metallic surfaces, were first patented in 1804. Aluminum eventually became the pre­dominant reflective material, but it did not achieve commercial popularity until the 1930s.2

The genesis of insulation board products dates to 1910. Two semirigid insulation products made from flax (a textile fiber made from plants) were manufactured in Minnesota, called Flaxlinum and Fibrofelt. These ultimately were replaced by rigid insulation board products, also first produced in Minnesota, in 1914. Insulite was manufactured by taking wood pulp waste products, known as sulfite screenings, and processing and drying them into a rigid, lightweight insulating material. This plant produced up to 60,000 square feet of Insulite per day.6 By 1920, Celotex Company intro­duced an insulating board made from bagasse, a waste by-product of sugar cane after the juice has been extracted.2 This was followed by Celotex’s Cenesto, a fire-resistant insulation board surfaced on one or both sides with asbestos cement, used primarily for low-cost housing.6 Lower-density insulation boards, generically belonging to the family of fiberboard products, were available in thicknesses ranging from 7Ae to Iм and in some cases up to 3". Fiberboard insu­lation commonly was used as an insulating lath over the wood studs, a plaster base over masonry, and even in some cases as an interior finish.6

The 1920s saw a measurable rise in public awareness of the val­ue of thermal insulation. While fiberboard was advertised as the most economical insulation of its time, batts began a rise in pop­ularity as well. Aluminum and copper also were applied to the batts as reflective foils.6 Slag wool is a material made by blowing steam through fluid slag (molten rock). Also known as rock wool, this product was later replaced by asbestos, similar in appearance and promoted as the best alternative by heating engineers who dealt with the control and handling of steam. Glass fiber produc­tion started in the mid-1980s.

The case also can be made that insulation was not as necessary prior to the 1920s as it is now because of the construction materi­als and methods used at that time. Materials were heavier, includ­ing windows and door sashes, which provided adequate weather resistance. The growing popularity and use of lighter building materials increased the need for insulation products.3 The gradual introduction of air-conditioning systems into home design also con­tributed to a greater need for thermal insulation.

In 1928, the Milam Building in San Antonio, Texas, became the first high-rise office building to be completely air conditioned. In that same year, Willis Carrier installed the first residential air con­ditioner, called the Weathermaker, that heated, cooled, humidified, cleaned, and circulated air in homes.7 One year later, in 1929, the Frigidaire division of General Motors introduced its first room cool­er. Several other manufacturers, including York and General Electric, began to offer room coolers soon after. The first window air conditioners were developed in the 1930s, but it was 1936 when Philco-York introduced a 3675 Btu/h window unit. Popularity increased throughout the next two decades, sales of window units approaching 300,000 in 1952. The early 1950s also saw the evolu­tion of smaller central air-conditioning systems, using water-cooled condensers, and they become more commonplace in residential use.8

During World War II, the use of building insulation was made mandatory to conserve metal required for heating and air-condi­tioning equipment and to save fuel.9 This probably contributed to a greater awareness by the general population of the sensible applications of insulation in residences as well. This was explored further by a special report developed by the Secretary of Defense in 1957. Capehart housing was rented to civilian employees at remote military institutions. The study concluded that if the 72,000 Capehart act houses would have been designed to suffi­cient thermal standard s, the United States government, which pays the heating bill as part of the rent, would save $52 million over a 30-year period.9

Extruded polystyrene insulation originally was developed by the Dow Chemical Company in the United States in the early 1940s. Known proprietarily as Styrofoam, it was first used as a flotation material in liferafts and lifeboats because its fully closed cell struc­ture renders it highly resistant to water absorption. The insulating properties of Styrofoam, combined with the advantage of the closed cell structure, led to its development as a thermal insulation mate­rial. Initial applications were in low-temperature situations for cold-store floors, wall, and ceiling panels and pipe insulation. In the 1950s, Dow’s extruded polystyrene foam extended its impact to other areas of the construction industry—as a thermal insultant in commercial and residential buildings.

The 1970s saw a dramatic shift in public awareness and sensi­bility toward energy conservation. The production of domestic oil had peaked in 1970, which subsequently created a greater depen­dence on foreign exports. Many researchers point to the Arab oil embargo of 1973 and 1974 as the catalyst for the energy crisis. A second sharp rise in oil prices occurred in 1979 following the Iranian revolution, further contributing to public discussion as well as new energy programs. Government mandates have continued this trend, with the Federal Energy Management Improvement Act (FEMIA) of 1988 requiring a 10 percent reduction in per-square – foot energy use by federal buildings between 1985 and 1995, fol­lowed by the sweeping Energy Policy Act of 1992 (EPACT). This act increased conservation and energy-efficiency requirements for gov­ernment, energy, and consumers. Federal agencies, for example, were required to attain a 20 percent reduction in per-square-foot energy consumption by 2000 compared with a 1985 baseline. All these initiatives contributed to a greater awareness of energy con­servation not only by the general public but also by producers, installers, and designers of insulation installation materials and methods.

As the U. S. paper industry grew in the 1940s, it was only nat­ural to look to paper by-products for insulation. Originally man­ufactured as a sound deadener, paper-based cellulose soon caught on as an effective, dense insulation material. Early cellu­lose insulation did not benefit from today’s fiber technology and application equipment, however, so it garnered only a small por­tion of the market as fiberglass became increasingly popular after World War II.10 (Cellulosic fiber insulation had several patents issued in the nineteenth century but gained little, if any, popularity.4)

As a result of the 1970s energy crisis, heavy demand for insula­tion induced many new producers to enter the cellulose industry, causing a resurgence of cellulose insulation popularity. Once the crisis passed, however, only a few companies remained committed to refining the material.11

Urea formaldehyde foam insulation (UFFI) was introduced to the building industry in 1960. Health complaints started from the occupants of UFFI-insulated homes in 1978, and by 1980, UFFI was banned across Canada, reportedly due to long-term health risk to occupants of houses insulated with UFFI. (Urea formaldehyde is one of the main resin mixtures of formaldehyde, and of all the formaldehyde compounds, it contributes the most to indoor air problems because of its water solubility.)12