On those hard plastic 3 ½" you could punch a hole an and format theme as 1.44mb. Roughly 10% of them could hold the data for more than few weeks.
Another twist with that. Writing with in 720 mode from a normal PC drive worked most reliably if the diskette first was formatted in the 720 PC.
It resulted in, after a couple of days, a lot of lost data. Luckily just games.