solarblack&#39;:
                material_name = self.solarblack
            if material_name in material_thickness.keys():
                material_thickness[material_name] += thickness.to(&#39;mm&#39;)
            else:
                material_thickness[material_name] = thickness.to(&#39;mm&#39;)
    res = {}
    for name, thickness in material_thickness.items():
        frac_mass, density = self.materials[name]
        mat = self.create_material(name=name,
                                   fractional_m