CORRECTION: The description originally stated that exposed film was to be used, but you actually have to use blank, developed film. A chemical used in the development process is what gives the film it's visible light filtering capabilities.
First off my apologies for the very shoddy camera work and even shoddier narration.
Secondly, this is merely my own personal findings after conducting several very unscientific tests using esotericsean's method of turning an ordinary camcorder into one that only lets in infrared light, allowing the operator to 'see through' various objects including clothing. The tests speak for themselves and yes, by using this method you can actually see what people are wearing under their clothing, provided that the clothing is relatively clingy, and is a thin fabric. Dark clothing works the best, but I've also gotten great results with all colors, provided that the fabric is thin and clingy.
The method: In case you haven't seen EsotericSean's video tutorial, the method is simple. You take any ordinary video camera with night shot capability, and you take a piece of BLANK, DEVELOPED film and put it over the lens. The film filters out all light other than infrared and the night vision disengages the infrared blocker in the camera. Now, if you want to be a little daring and don't care about using the camera normally ever again you can try removing the IR blocker from the camera entirely, although some people have said that it screws up the focus.