Thermos almost lost its trademark for being too successful.
James Dewar invented the vacuum flask in 1892, never patented it, and never profited from it. Glassblower Reinhold Burger patented a home version, and a Munich entrant won his naming contest with “Thermos,” Greek for heat. The word caught on so completely that in 1963 a US court ruled lowercase “thermos” plain English.
Thermos on Brandseum