These panels come to us from Voltaic Systems, makers of fine solar-powered bags and packs. These are waterproof, scratch-resistant, and UV-resistant, and they use 10 high-efficiency monocrystalline SunPower cells with 22+% efficiency (praise the sun!). Each cell has a nominal voltage of 0.5V, so we call this a "5V" panel. Note the datasheet has it down as a 6V panel, because at max-power-point it will give you 6.1V