This is from Courant and Robbins, "What is Mathematics", pg 214 * * * One of the most remarkable properties of the hyperboloid is that although it contains two families of intersecting straight lines, these lines do not make the surface rigid. If a model of the surface is constructed from wire rods, free to rotate at each intersection, then the whole figure may be continuously deformed into a variety of shapes **** So, I'd like to play with such a model. Can I buy one somewhere? Does anything come to mind? I doubt I have patience to make one. I'm also a bit unclear on what "free to rotate at each intersection" means in the quoted passage. Can you fold it into nonhyperboloids? Google was unhelpful. Here's a photo from the book http://static.flickr.com/37/104048548_2327835121_o.gif -- Thane Plambeck http://www.plambeck.org/ehome.htm