All substances emit thermal radiation (at temperatures above absolute zero). Nevertheless, for any specific temperature and wavelength the total emitted thermal radiation is determined by the emissivity of the substances surface.
Emissivity of materials is defined as the ratio of the energy radiated from a substance's surface to the energy radiated from an ideal emitter (blackbody emission/ black body radiation) under the same conditions. It is a value between 0 for an ideal reflector and 100% for an ideal emitter.
The surface emissivity can be changed by applying appropriate coating, for example high emissivity black paint and black anodize. Acktar vacuum deposited black coatings (PVD thin films) reach nearly ideal infrared emitter value: 98.5% - blackest material with highest emissivity at the industry for coating thickness of just 5 microns.