Abstract: The reflection and transmission coefficients are determined and compared using CST MWS (Computer Simulation Technology Microwave Studio) 2014 Software for two different materials. The materials are Arlon Iso 933 with Epsilon 2.33 and El. tand 0.0016 and the other Gil GML2032 with Epsilon 3.2 and El. tand 0.0029. Additionally, whole previous calculations of parameters are determined in the range of frequencies of X-band. The results show that the reflection and transmission coefficients directly proportional with dimension=s value of the layer. It seems that the reflection coefficient has one minimum value when the layer made of Arlon Iso 933 while has two minimum values when the layer made of Gil GML 2032. The transmission coefficient is recorded a good value at same frequencies. With the minimum value of reflection coefficient and maximum value of transmission coefficient, the absorption coefficient is a pproximately 53% is measured in Arlon Iso 933 material while in Gil GML2032 material, the absorption coefficients are 56, 63%, respectively.