Czechoslovakia - Austrian Definitives- Faserpapier

Hi!
I have already read about granite paper in a previous post and I have searched also about Czechoslovakian stamps. Still I have doubts about what "faserpapier" means in the case of Czechoslovakian stamps, specifically Austrian definitives "Imperial crown, emperor Franz Joseph, coat of arms".
There are three types of paper for these stamps, the initial one, with different colors and with "faserpapier". In the catalog (Valuable stamps of the world) I have, "faserpapier" is translated as paper with silk fibers ("granite paper").
How can I identify this "faserpapier" for this Austrian definitives?
I have some photos but the stamps do not belong to me.
Unfortunately I cannot provide better photos.
Thanks in advance for your help.

It's pretty distinctive - this issue with the granite paper/faserpapier has many little blue silk "threads" clearly visible on both the front & back of the stamp. I can post a picture later if needed. The ones you're showing are ordinary paper. In terms of Michel numbers, the ordinary paper 4k is Mi 206 issued in 1917, faserpapier 4k is Mi 210, issued in 1919.

~Greg

Faser paper


https://stampauctionnetwork.com/CL/cl6104.cfm

Thanks a lot!

RACINES ---- Wanted the experts to help you first . Because I am no expert ,I am just a lickem-and-stickem collector .

But since they gave you a different answer than me ,here is my pages on that stamp plus here is my take , first not sure your stamp has the correct over print ,I would have to get out my forgery collection to call it a original overprint .

Your stamp paper looks to be type II paper .

@floortrader
Now I am confused

I must admit that I checked the paper thickness with a depth gauge and the thickness was different for different stamps. It is easy to feel the difference between different stamp papers just using the fingers. The paper looks like having some "waves" on the back side but it can be just the glue...

I have some other stamps from the same set. The paper color is different between what I though it should be faserpapier (greyish) and normal paper, the paper thickness is also different but there are no black silk threads.
I have one stamp with black threads with a different overprint (in the image below). The black threads can be easy seen both on back and front side.