A sheet type balloon has a blank, colorable area partly formed on an outer
surface of a body, so the balloon is available for coloring or studying
materials as well as typical playing materials. The balloon further has a
valve assembly having bi-directional functions, i.e., deflation and
inflation of the balloon. To inflate the balloon with air or gas, a
fastener of the valve assembly is open by separating a convexly
protruding line and a concavely protruding line. After inflation, the
fastener is closed by apply a pressure to both protruding lines, so the
protruding lines are closely combined and thus intercept the outward flow
of inflating air or gas within the body. Then, for carrying or reuse, the
fastener can be open again by separating the protruding lines.