Bricks exhibit a range of physical properties based on their composition. The typical attributes of a fire-baked brick include a density between 0.06 and 0.1 pounds per cubic inch, an R-value of 0.2, a specific heat of 1 joule per degree Celsius difference, and a compressive strength between 7 and 80 megapascals.
Bricks frequently contain a combination of sand, clay, lime, iron oxide and magnesia. Different manufacturers have come up with other combinations throughout history, with differences in available local resources usually being the deciding factor. Since the advent of global industrialization, standardizing brick composition and dimensions throughout the world has been a difficult task. Bricks manufactured in the United States adhere to standards set forth by the American Society for Testing and Materials, while those manufactured elsewhere do not.
Builders commonly use bricks because of their high compressive strength. While common red clay building bricks exhibit compressive strength between 20 and 40 megapascals, construction materials companies constantly strive to develop better, stronger materials. The strongest bricks available in the 21st century can reach a compressive strength of 80 megapascals, well above the strength of the world's most famous bricks, the red Accrington bricks used in the 1930's to lay the foundation of the Empire State Building.