The helmets, mass-produced by a Dutch manufacturer, are made in different colors and bear slogans to fit the different countries attending the tournament.
Designer Weno Geerts said they were meant as a joke. "We just want to support our team and tease the Germans. Nothing else," he explained.
Geerts said the Holland-based company had received only a few complaints and expected to sell another 100,000 helmets before the finals this summer.
"They are meant for the supporters who watch the games on television, and in the pub, and also those who are traveling to Germany," he said.
The manufacturer of the helmets said the German police recently informed him they intend to allow fans to wear the helmets during the games, because they were not adorned with Nazi symbols.
"Germany should prepare for an invasion," he said jokingly.