The penetration of infrareds
Just like sound propagation (Low-frequency sound propagation in the air, the air molecule vibration is small, the friction is slower, less energy consumption, so distant spread, transparent and full of vitality.) The penetration of infrared wave has an feature: The infrared wavelength will be reverberation, refract or absorption when wavelength is short than Obstacle. The infrared wavelength is a continuation of penetration(wave got round the penetration) when infrared wavelength is big than Obstacle.
These two examples duplicate each other.
1、Studies show that infrared wavelength quickly permeates plastic packaging material. the visible light was the same. Because of the infrared wavelength is big that visible light wavelength .when the visible light can’t cross Obstacle, the infrared wavelength still less penetrating  Obstacle .
2、Due to the infrared wavelength（0.78nm-1000nm） is also relatively long . the water droplets suspending in cloud are often larger than the infrared wavelength . so the infrared wavelength were able to bypass their .