How can you tell if a material contains asbestos?

The ONLY way to determine for certain that a material contains asbestos is to have it tested in a laboratory. In Ontario, the minimum number of samples required for testing in most cases is 3, with the exception of plaster where it can be 3, 5 or 7. There are some materials that may be ASSUMED to contain asbestos though as they are consistently found to contain asbestos. These are things like certain pipe insulation, duct insulation and flooring.