The Frequency Selective Surface (FSS) design structure consists of square FSS placed on the FR4 and energy saving glass (ESG). Then, the circular and square slot FSS is added on the square FSS to produce a dual band FSS. The FSS design structure is designed and simulated by using the CST Microwave Studio software at 2.4 GHz and 5.2 GHz frequency response based on industrial, scientific and medical bands (ISM) standard. The reflection (S₁₁) and transmission (S₂₁) of the design FSS structure is analyzed and the effect of the material used is studied. The material of the substrate affects the transmission and reflection signal of the FSS. The dual band FSS is designed on the ESG to improve the transmission of the WLAN signal at 2.4 GHz and 5.2 GHz.