Hi Frans,
Because finding good marker tape can be cumbersome, I would like to mention this one to you, if you would be interested. It is great, I love it because it is a bit solid (instead of some too flexible tape), rips of easily and is perfect to write on with anything. I prefer a CD marker pen. I also use it to label my looms. And as a bonus, it is pretty cheap.
http://www.thomann.de/nl/stairville_beschriftungsband.htm