M1 stands for low emissions.
The classification divides building materials into three categories, of which M1 is the best. The M1 label states that the product has been tested in an independent and impartial laboratory, and that it has met the specified criteria in a age of 4 weeks.
M1 is a Finnish indoor climate system, managed by the Building Information Foundation RTS sr. As on the basis of tests by i.a. The VOC emission makes it possible to compare and assess the impact of different building materials on the indoor climate in a building.
The system has 3 emission classes for low emission products, with M1 being the best grade of the three.