W 300 type water vapor permeability analyzer ensures the high precision of the testing results with its accurate electromagnetic balance type weighing cell and the circuit handling. It can precisely control the temperature and simulate the humility, and use the principle of the weight method to make the W 300 type become the optimal choice for testing and researching the packaging materials. On the basis of the control software of the standard Windows, the operation of W300 is convenient and of high efficiency. The remarkable feature of this instrument is that it can display the real time vapor permeability direct-viewingly in test process, which conforms to the GB/T1037-1988.