What is the difference between IR and ND filters?

Question

What is the difference between an infrared filter and an ND filter? I have a big stopper and I would like to take some images to show the infrared spectrum I have seen images where green foliage shows up red and any heat source shown up white §Is there any lens filter recommended for this genre of photography

Answer 1

ND stands for "neutral density" - it is a filter type that (in theory) absorbs all wavelengths of the visible light by the same amount.

^{Effect of a ND-filter. CC-BY-SA 2.0: Robert Emperley}

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IR filters filter out all but certain wavelengths - the (near) IR wavelength of the filter. So basically, they are IR-pass filters, not IR-block filters. ^{Thanks @TheLuckless!}

As @Hueco states in his comment, IR filters will cut everything below a certain value. That value might be between 650 and 720nm - visible light, however, does go up to 750nm. ^{Thanks for clarifying that, Hueco!}

^{Typical result of using an IR filter. Some effort was put into post-production: The red and blue channels were swapped. CC-BY-SA 2.0: Jannis}

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What you think of (white heat source, everything else red-ish) is most probably a thermographic camera - they differ from regular cameras in a lot of ways, including lenses that are (typically) made out of Germanium.

^{Thermographic image. CC-BY-SA 3.0: Lutz Weidner}