A Soleau envelope, named after its French inventor, is a sealed envelope serving as proof of priority for inventions valid in France. It is used to ascertain the date of an invention or creation. It is comprised of two compartments each one of which contains an identical example of the work or creation such as a description, design or photograph.
The sealed envelope is sent to the INPI who proceeds to registering it. The INPI sends one of the compartments back to the registering party and keeps the other for a period of five years during which time it can only be renewed once.
While a Soleau envelope is useful in the sense that it attests to the date of creation of the work, it is important to bear in mind that it does not accord any industrial property title.