FRANKFURT — Luigi Colani, a German designer known for applying sensuous shapes from nature to high-tech objects like supersonic jets and super sports cars, died on Monday in Karlsruhe, Germany. He was 91.

His death was confirmed by Albrecht Bangert, who wrote the 2004 book “The Art of Shaping the Future” with Mr. Colani. He did not specify the cause, saying only that Mr. Colani had been severely ill.

Many of Mr. Colani’s best-known designs were considered too far out for mass production. One, for example, was for a long-haul truck in which the driver sat inside what looked like a plexiglass flying saucer.

Some members of the German design establishment said his work was overdone, utopian or simply impractical. Yet others considered him a visionary in an unimaginative world: His fanciful work was displayed at major museums like the Pinakothek der Moderne in Munich and the Centre Pompidou in Paris. In 2007 the Design Museum in London staged an exhibition of his work.