How do you block infrared cameras?

I don't have a very complete answer, but I've been looking into this.

Some things that either absorb or reflect infra-red light:

-Plexiglass

-Water

-Some Mirrors

-The coatings of some cool-colored light-bulbs.

-Some Red Paints

-A cloth that gets especially hot in the sun. It's hard to tell with black cloth, because it absorbs so many other spectrums of light. If you find a light-colored cloth that for some reason gets hotter in the sun than other cloth, it probably absorbs infra-red.

-The effect of Aluminum foil may be useful in distributing heat and blocking.

-Some sunglass lenses

-Most Plants

There are some other substances and filters that are kinda hard to find or use, but apparently, some Japanese company is making underwear that blocks infra-red.

see:

http://gizmodo.com/gadgets/japan/Japanese-anti+pervert-panties-block-ir-284523.php

Apparently they're made of nylon and polyurethane.

Hope that helps!