We analyze the stability of 3D structures composed of heat-shrinkable polymer sheets and thin plastic sheets floating on water surface. Sheet materials have the advantages of the lightness and the ease of deformation. Because of these advantages, the sheet materials are used in robotic parts that float on water surface by the surface tension such as a camphor ship. We propose a new method to realize self-folding sheet materials on water surface using the heat-shrinkage of polymer sheets. The use of heat-shrinkable sheets for self-folding on water surface is difficult for the specific heat of water, and we adopt a 2D sheet structure for self-folding. Our method enables the remotely-operated deformation from the 2D structures to the 3D structures on water surface. The deformable 3D structures are able to adapt to different water surface conditions. In this study, self-folding speed is compared using heat-shrinkable polymer sheets drawn in two colors. Two types of 3D structures are prepared by considering the difference in self-folding speed depending on the color. We finally evaluated the stability on water surface of the two different 3D structures.