The paper reports the design and fabrication of solid samples to form a heterogeneous breast phantom that can be used to test the effectiveness of an ultrawideband (UWB) microwave imaging system in the pre-clinical stages of breast cancer detection and location. The investigations aim at achieving electrical properties, specifically the dielectric constant and conductivity, of these materials to represent both low and high density breast tissues. The tests performed on the fabricated samples show that they have the required electrical characteristics. The investigations are concluded with the fabrication of a hemispherical breast phantom representing the mixture of fibro-connective, glandular and adipose tissues ready for testing the imaging system in the 3 GHz to 11 GHz frequency band.