For RF absorption, the rule of thumb is that the higher the frequency, the more the signal is attenuated. Once you get into the gigahertz range, things like lea

For RF absorption, the rule of thumb is that the higher the frequency, the more the signal is attenuated. Once you get into the gigahertz range, things like leaves block (actually: absorb) a huge amount of the energy. This is why if you have a wifi router with both 2.4 and 5 GHz bands, the 2.4 GHz band usually has much better range. Visible light is in the THz spectrum which is blocked by anything solid that isn't clear or translucent.