Test is run with bars one half inch wide by five inches long. These are held horizontally and exposed to a laboratory burner flame three quarters of an inch high. Ignition is forced until one inch of sample has burned, the flame removed, and the burning rate is measured.
To pass ULHB a sample over one eighth thick must burn slower than one and one half inches per minute, and a sample one eighth inch thick or less must not burn faster than three inches a minute. This is very similar to DOT MVSS 302.
