French designer Philippe Starck has derided Eurostar passengers who dress in comfy clothes for the trip across the channel.
Eurostar want people to think 'wow' when they travel on the train
Mr Starck, who is re-designing the train service, said he wanted people to be a bit more stylish.
"There is a tendency today for people to travel wearing purple jogging bottoms, green fluorescent sweaters and orange Nike trainers," he told the Times newspaper.
"I can understand that people want to be comfortable, but it is possible to be elegant as well.
"Sometimes you open a little door to people and they will be inspired to upgrade themselves."
Sometimes you open a little door to people and they will be inspired to upgrade themselves
But Eurostar spokesman Roger Harrison stressed people were still welcome on the train no matter what they wore.
"We're not imposing a dress code. What we are trying to do with this is make people think 'wow, I'm going on Eurostar.'
"Smart casual, loose casual, anything goes," he told BBC News 24.
Mr Starck - dressed in blue jeans, a suit jacket and white trainers when he made his comments - is set to modernise the train interiors as part of a £35m refurbishment in the face of falling ticket sales.