How is it absorbing instead of reflecting energy?

Do things store energy when they absorb [mmWave] EM? As phonons?

Twisted Single Walled Carbon Nanotubes store energy;

From "LG Chem develops material capable of suppressing thermal runaway in batteries" (2024) https://news.ycombinator.com/item?id=41745154 :

> "Giant nanomechanical energy storage capacity in twisted single-walled carbon nanotube ropes" (2024) https://www.nature.com/articles/s41565-024-01645-x :

>> 583 Wh/kg

From "Gamma radiation is produced in large tropical thunderstorms" (2024) https://news.ycombinator.com/item?id=41775612 :

> "Sm2O3 micron plates/B4C/HDPE composites containing high specific surface area fillers for neutron and gamma-ray complex radiation shielding" (2024) https://www.sciencedirect.com/science/article/abs/pii/S02663...

> Abstract: The revolution of millimeter-wave (mmWave) technologies is prompting a need for absorption-dominant EMI shielding materials. While conventional shielding materials struggle in the mmWave spectrum due to their reflective nature, this study introduces a novel EMI shielding film with ultralow reflection (<0.05 dB or 1.5%), ultrahigh absorption (>70 dB or 98.5%), and superior shielding (>70 dB or 99.99999%) across triple mmWave frequency bands with a thickness of 400 µm. By integrating a magnetic composite layer (MCL), a conductive patterned grid (CPG), and a double-walled carbon nanotube film (DWCNTF), specific resonant frequencies of electromagnetic waves are transmitted into the film with minimized reflection, and trapped and dissipated between the CPG and the DWCNTF. The design factors for resonant frequencies, such as the CPG geometry and the MCL refractive index, are systematically investigated based on electromagnetic wave propagation theories. This innovative approach presents a promising solution for effective mmWave EMI shielding materials, with implications for mobile communication, radar systems, and wireless gigabit communication.