Apparently, there are two types: one for OHP pens, and one for
laserjet printers. They have slightly different textures or
something, I suppose.
I just learnt this a couple of weeks ago when I wanted to buy
transparencies and another auntie asked: 'For writing or for
printing?'
Print transparencies can damage the OHP pen tip, it seems.... at
least, now I can't seem to write using the OHP pens.

what era liao
still using transparencies 
i thought they should have moved forward to the image projection
gadget
that's what we use for briefing at work last time