Styled in a closed-back design, the RPmk3 Series T40RPmk3 from Fostex comprises a pair of stereo headphones. Their copper-foil etched polyimide film drivers utilize proprietary Regular Phase (RP) technology in order to ensure an accurate reproduction of sonic material, thereby rendering these closed-back headphones suitable for monitoring in studio situations. To ensure a full representation of the sonic spectrum, these headphones have a frequency response of 20 Hz to 35 kHz.

The RPmk3 series is an evolution of the RPmk2, and as such, features redesigned housing, head-pad, and ear-pads to further both comfort and maximum performance of the RP driver. These headphones are designed to highlight a more focused low-end, and sport a detachable cable, which can be replaced if lost or broken.