Like Aargau, Thurgau was historically a subject territory of the confederacy, and was created as a canton of the Helvetic Republic. The flag design is an ad-hoc creation of 1803, based on the two lions in the coat of arms of the House of Kyburg which ruled Thurgau in the 13th century. The green-and-white were regarded as "revolutionary" colours in 1803, also introduced in the coats of arms of St. Gallen and Vaud, but the placement of a yellow lion on white is a violation of heraldic principles, and also creates a visibility problem. There have been suggestions to correct this, including a 1938 suggestion to use a solid green field divided by a diagonal white line, but they were not successful.
Most mass-produced flags are commonly 150x90cm / 5x3' or 90x60cm / 3x2', which will often vary from the official size ratio. We now offer a custom-manufactured official size option for our many of our flags.