9x12 cm holder question

I recently got 3 9x12 cm film holders to fit my ICA Ideal.

After checking the forums here, on photo.net, and a google search it seems that I either need "film sheaths" for them or need to somehow fit a 1mm plate of 9x12cm glass in them and feed the film over that plate.

If this is correct (and if it's not, please correct me!), this begs the questions:

1) Can the film sheaths be made? I can't find any on eBay to save my life.
2) If I have to use glass, is any particular kind of glass preferable?

Thanks!

1) Yes they exist, but they can be difficult to find. There are far more plate holders in the world than there are film inserts. The sheaths can more easily be found in Germany than anywhere else in the world, but it takes time. A "shortcut" is to get them from Peter Karl Jonas in Austria. They're calles "Cutfilm holders" in the English catalogue. Get one, and copy it. Or since the postage will be the same - get as many as you need.

2) It should be thin, and not very flexible. Glass is great for larger sizes - 5x7" and up - but I've found it difficult to use in the little 9x12cm plate holders. YMMV.