Afortunadament, és possible construir un cos negre pràcticament perfecte. Es construeix una caixa amb algun material que sigui termoconductor, com ara el metall. La caixa haurà d' estar completament tancada per tots costats, de manera que l' interior formi una cavitat que no rebi llum des de l' exterior. Aleshores es fa un petit forat en algun punt de la caixa. La llum que surti d' aquest forat tindrà un semblant gairebé perfecte al de la llum d' un cos negre ideal, a causa de la temperatura de l' aire a l' interior de la caixa.
Fortunately, it is possible to construct a nearly-perfect blackbody. Construct a box made of a thermally conductive material, such as metal. The box should be completely closed on all sides, so that the inside forms a cavity that does not receive light from the surroundings. Then, make a small hole somewhere on the box. The light coming out of this hole will almost perfectly resemble the light from an ideal blackbody, for the temperature of the air inside the box.