A method for using a Poisson's ratio material includes a carbon nanotube film structure is provided. The carbon nanotube film structure includes a plurality of carbon nanotubes. A first part of the carbon nanotubes are aligned a first direction, a second part of the carbon nanotubes are aligned a second direction. The first direction is substantially perpendicular to second direction. When the Poisson's ratio material is stretched or compressed substantially along the first or second direction, a Poisson's ratio value is negative. When the Poisson's ratio material is stretched or compressed in a direction having an angle of about 45 degrees with the first direction, the Poisson's ratio value is positive.