We present a new composite material containing calcium alginate microspheres incorporated into an epoxy matrix. The new material is mechanically stable and does not degrade over time. Its di-electric properties are extracted by model calculations and compared to the properties of some selected human tissues. Good agreement is observed, which identies the proposed composite material as a good candidate for the use as a phantom material. The presented material is a two component composite and it is shown how its effective properties can be predicted by using appropriate mixing formulas.