Here is my attempt at a definition: When you bend a sheet of paper, the fibres on the mountain side are stretched and the fibres on the valley side are compressed. This causes tension in the paper which tends to revert itself back to its original flat form. Wetting the paper reduces the tension and the paper when dried will keep to its bended form.
How then can you fold the paper such that the bended or curved form is maintained without wetting the paper? You can fold the paper such that you have two curved surfaces intersecting along a curved line. This is done by folding the paper with an intrinsic straight and an intrinsic curved crease. There is an overlap of paper between the curved and straight crease and the tension on the two curved surfaces in shape without wetting and drying. You can have more than two curved rigid surfaced by such tension folding. Below is a form consisting of three curved surfaces by dry tension folding: https://www.flickr.com/photos/chengchit/920472460/in/dateposted-public/ And a Seal model by dry tension folding: https://www.flickr.com/photos/chengchit/920461244/in/dateposted-public/ Cheng Chit
