The school of aerospace of Tsinghua University has started a project to develop new kind of stratospheric balloons for earth observation. These balloons will be designed to stand in the same position during a few days at 20 kilometers of altitude. To reach this goal, the first step is to select adapted materials for the balloon envelope. The materials for stratospheric balloons application should have specific properties adapted to the environment such as mechanical, thermo-optical, and permeability properties. Thus, we have asked a material manufacture company to develop and manufacture a material adapted to our application. In this paper, we will present the first results concerning the mechanical properties of the material. Experimental facilities have been developed to test the mechanical behavior of the materials at room and low temperature. The future development of the project will be to identify behavior law adapted to our material that fits with the experimental results.