Futon in Japan

Last week 3 of my friends from Germany visited me in Fukuoka. Of course I told them before to stay at my place, so they don't need to book a hotel. I also mentioned that I have 4 futon-beds which they can use. They wondered and guessed my apartment must be big. But when they entered my place and saw the traditional futons they got shocked. "Oh Mike"..."didn't you say we could sleep in a futon-bed?", they said. "Yeah, actually this is a traditional futon", I answered. But German futons a completely different from a Japanese one, they look like a real bed and you can't fold them. Oh no, I forget to tell my friends about the differences^^