My guess is that it is just a plastic that is IR-transparent and visible-opaque, viewed by a camera with no IR filter. Actually fairly common - coke cola is IR-transparent. Not sure you can get an image through it, but I wouldn't be surprised.
Yup, you can see through Coke by opening up a cheap webcam and removing the IR filter. You can even make an IR-only camera by replacing the filter with a piece of exposed film, which is black in the visible spectrum and but lets IR light through. http://www.hoagieshouse.com/IR/
Most black plastics become transparent fairly quickly in the near-IR, it's something the dye designers aim for since it reduces the heat load into the material and makes it last longer.
Doing this with a regular (IR filter removed) BW camera and a polythene garbage bag is a standard science-fair demo.
As you get further into the infrared it becomes annoying. lots of things you think of as black, like black anodize and black electrical tape are transparent - so you get reflections and light leaks from things you would never think of.
