Abstract <p>A composite material based on polyethylene, boron carbide (B₄C), and bismuth oxide (Bi₂O₃) is synthesized by the method of joint cryogenic milling of all components in liquid nitrogen environment followed by pressing. The effect of cryogenic milling on the distribution of fillers in a composite is studied and the prospects of using this method are assessed in comparison with traditional methods of mixing components of polymer composites. The structure and properties of the finished composite are studied using scanning electron microscopy (SEM), IR Fourier spectroscopy, and X-ray phase analysis. The strength characteristics of a composite material with different filler contents are determined. It is shown that the optimal composition is one containing 55 wt % of polyethylene, 5 wt % of boron carbide, and 40 wt % of bismuth oxide, which provides a good balance of strength. Cryogenic milling results in a uniform distribution of filler particles in the matrix and improves strength characteristics of the material. The composite is stable up to 250°C and has high thermal properties, which makes it to be promising for use in space constructions requiring materials with high heat resistance and radiation protection.</p>