N95 masks are so named because they filter out 95% of the test particles. Surgical masks stop about 40%. I read an article recently that said most of the ad hoc cloth masks tested stopped 0-10% depending on material (mostly related to thickness).
There is nothing special about diapers, they are thick so probably would stop more than a thin piece of cloth. Also would be very hard to breathe through, and if you aren't restricting air to passing through the diaper then they are doing nothing.
Be aware there are studies which have found the use of cloth masks can increase infection rates. This 2015 study found hospital workers wearing cloth masks had a higher infection rate than the control group who wore masks only as recommended by policy (used dealing with patients who were suspected of cold / flu like illnesses). This study also found most cloth masks only stopped 3% of the test particles.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4420971/
The primary reason for suggesting face masks is to help reduce the wearer from spreading illness, they offer almost no protection for the wearer.
This is why there is resistance to requiring masks, they offer a high chance of providing a false sense of safety and can lead to people being less cautious. Your #1 means to stay healthy is to avoid people, be obsessively aware of your hands, what they are touching, and keeping them away from your face and compulsive hand washing.
Also the cheap paper dust masks you see many wearing have no rating, they are considered nuisance dust masks and are probably no more effective than a DIY cloth mask.
