Multiple Input Multiple Output (MIMO) systems are increasingly used to support the rapid growth in mobile traffic. Their ability of multiplying the data capacity is especially suitable in 4G-5G wireless railway communications. However, MIMO efficiency is limited by signal power, signal to noise ratio and channel condition number. This paper presents a novel insulating glazing particularly relevant for MIMO technology in telecommunication. Our glazing delivers high throughput thanks to low attenuation (< 6 dB) and fair transmission loss imbalance (< 6 dB) between the orthogonal E-/H-polarisations over a large range of incident angles and gigahertz frequencies. To achieve this, low relative permittivity materials are assembled in transparent multilayered glass panes to form an insulated glazing. A conductive coating is deposited to create a Frequency Selective Surface (FSS). The microwave transmission and MIMO efficiency are then studied for different configurations. Using the novel glazing, the data throughput at high angles of incidence can be increased by a factor up to 4.5. The presented results show an important improvement compared to soda lime glass glazing and meet operating requirements of antenna corridors. Our glazing shows a strong added value concerning MIMO efficiency in railway telecommunication, opening an alternative way to signal amplifiers.