[qmcgraw]

You need a video camera with a night vision mode that you can turn on and off manually and an special filter which only allows infra-red light to pass.

Basically, Infra-red has a long enough wavelength that it can pass through thin clothing. The filter only allows infra red through. Night vision mode on cameras pick up and amplify light. Therefore you get a wierd see through effect on thin clothes.

It only works outside though, on very sunny days, because indoor lights do not produce infra-red light.