Screenshot from the YouTube channel Thunderf00t
This guy shows a fun experiment when dealing with infrared cameras. Did you know that they could see through trash bags for example?
On the screen we can see two different views from the camera, one showing the visible light and the other one only what we can see through an infrared camera.
To become invisible to the infrared camera, he shows how you can use a sheet of paper or even Plexiglas. That's right, something that would let the normal light go through won't let someone behind an infrared camera know you're there!