Abstract: A hot/cold therapy and light therapy (phototherapy) provide synergistic effects for a user. An improved gel pack is provided wherein a flexible circuit with at least one light source is provided. The at least one light source emits light through the gel and onto the target treatment area. The flexible circuit is sealed and embedded in the gel pack to allow the gel pack (including the flexible circuit therein) to be washed and cleaned easily. Furthermore, the improved gel pack may be assembled in a layered structure to provide the waterproof gel pack, e.g., sealing the gel in the gel pack and embedding a flexible circuit in the gel pack. To improve durability, the flexible circuit may be supported by a layer which forms the outer covering of the gel pack.