Stage lighting gels must be transparent to IR or else they will get too hot and melt. So if they can be stacked to block visible light, then only IR is going to get through them.
Digital cameras are naturally sensitive to IR. In fact, they need IR blocking filters to keep the appearance of their images looking like we expect. Now the camera must adjust its exposure time to compensate for the purely IR image, but my dissertation camera can handle it. I'll have to look into the effects of increased exposure time and the unsteady tripod that a BalloonSat simulates. However, if this is not too much of an issue, I expect two cameras, one with IR filter and one without, to make a great near space experiment for students.
This is the infrared image taken on Thursday afternoon. Notice how bright the tree leaves appear. Chlorophyll is very reflective in IR. Also note how much brighter the trees are than the apartments behind them in IR (but not visible).