Which one is a better option (to block more visible light and to block less IR light), floppy disk or developed unexposed photographic film?
There are lots of DIY IR-pass filters...
- Stacking colored gels (colored transparency sheets).
- Stacking ND filters.
- Crossing polarizing filters.
- Variable ND filter.
- Floppy disk – particularly poor because of metal content.
- Developed color film. Unexposed if reversal (slide film). Exposed if negative. – Undeveloped and B&W films won't work well because of metal content.
None of them is as good as cheap IR-pass filters. They come in different frequencies that have slightly different effects. 720nm is the most commonly recommended.
If you are shooting digital, modify your camera for "full spectrum" capture. There are inexpensive premodified compact cameras available for sale online.