Materials that efficiently absorb and accumulate heat vary based on their specific heat capacity, which determines how much energy is needed to raise their temperature. Metals, with low specific heat, require less energy to heat up, while substances like water have a high specific heat, making them better at storing heat. Helium is considered for use in fuel cells due to its high heat capacity and lightweight properties, although its effectiveness depends on the design specifics and thermal time constant. The discussion emphasizes the importance of understanding the intended application and the relationship between heat capacity and thermal conductivity. Ultimately, the choice of heat absorber should align with the goals of trapping waste heat effectively.