The process writes on dimensionally stable films, often silver halide or photopolymer
https://www.newsbreak.com/dmr-news-321522575/4524631068041-artnet-pro-sets-the-standard-in-high-resolution-pcb-photoplotting-for-aerospace-and-advanced-electronics
The process writes on dimensionally stable films, often silver halide or photopolymer, creating opaque and clear regions that guide UV exposure of photoresist during PCB imaging and subsequent development.