The effects of adding a thin layer of an energetic polymer such as nitrocellulose (NC) to laser photothermal imaging media are investigated. Photothermal media are used which are model systems for computer-to-plate or computer-to-press imaging. The media consist of a substrate, a thin absorbing metallic absorbing layer and a silicone rubber imaging layer. An energetic polymer can be added between the substrate and the absorber. With 10 μs duration near-IR exposure pulses, the energetic layer has no discernable effect. With 110 ns imaging pulses, exposed spots in imaging media with energetic underlayers can be more than three times larger. The improvement due to energetic polymers results from confining the hot gas-phase thermochemical decomposition products under the silicone layer, as shown by time-resolved microscopy. The force exerted by the expanding bubble tears the neck of the bubble away from the substrate, increasing the imaged spot size. These rather complicated processes cannot be described by previously used simple exposure threshold models. An exposure parameter is introduced which deals with this problem. In some cases energetic material underlayers can improve the sensitivity of the media by a factor of three. This work is believed to be the first where a substantial sensitivity improvement in laser threshold for photothermal imaging is obtained with energetic polymers.