Infra-red film is sensitive to light in the near infra-red part of the spectrum. Usually, the film will be sensitive to visible light as well; an IR filter will block all but the IR wavelengths.

The film isn't easy to use. For starters, the little felt trap on the film canister will not shield the film from infra-red light. Therefore, complete darkness is needed to even load the film into the camera. That can be a royal pain in the glutes. A ten-second operation under normal circumstances; I have fought for over 15 minutes to load the camera a few times. The urge to turn on the lights is overwhelming; that would ruin the film, however.

Secondly, with an IR filter on, you can't look through the view finder to compose your shot; it blocks out visible light, and is almost 100% opaque. And most lenses will focus IR wavelengths a bit differently than visible light; unless your lens has a marker to denote where to focus for infra-red, you have to guess-timate. There's a formula somewhere. To top it off, the light meter within the camera is set for the visible part of the spectrum; getting the right exposure with IR film is a mixture of art, science, and voo-doo.

It's worth the hassle, in my opinion. Any vegetation with chlorophyl turns bright white. The blue sky turns very dark, while clouds stay white. Skin becomes pale and subcutaneous veins may show. The eyes -- the entire eyeball -- appear jet black.

Now that I think about it, I kind of miss shooting with infra-red. There's a few rolls in my freezer, if I remember correctly.

[Note to self: get on it!]