Breast Microwave Sensing (BMS) systems require adequate testing and performance before reaching clinical trials. This thesis presents improved materials for shell-based breast phantoms and quality assurance devices to provide comparable testing in the field. Previous studies utilized 3D-printable plastics to create shells for shell-based phantoms; however, the low permittivity of these plastics impacts the phantoms’ dielectric accuracy. The liquids filling shell-based phantoms also often contain air bubbles, leading to undesirable microwave scattering. This research explores new tissue-mimicking materials to overcome these issues. The low-permittivity 3D-printed plastic filament have been substituted with graphite, carbon black, and resin to replicate the skin’s properties within the 0.4-9.0 GHz range. Diethylene Glycol Butyl Ether (DGBE) solutions have replaced glycerin and Triton X-100 to simulate the characteristics of adipose and fibroglandular tissue. The resin-based material more accurately mimicked the properties of ex vivo tissue samples than 3D-printed plastics. DGBE solutions demonstrated superior dielectric properties compared to glycerin and Triton X-100 solutions. These DGBE solutions are preferable over glycerin and Triton X-100 due to their lower viscosity, reduced tendency for air bubble formation, better short-term stabil-ity, temperature stability, and enhanced long-term stability, which supports the reusability of these materials. Quality assurance devices were designed and 3D-printed to analyze and compare BMS systems, an area the field has been lacking in the literature. The materials studied in this work improve on existing breast phantoms by ensuring dielectric accuracy and stability, offering better experimental utility for microwave breast imaging. At the same time, the devices presented can be used for quality metrics to appropriately compare BMS systems on a fundamental level.