I am currently in the process of making some flash product of my own. I do have the chemicals required and safety gears.
The reason I decided to manufacture my own flash products is because the import restriction from usps. I know some guys in my country who also manufacture their own flash paper. But instead of using paper, they use tissue. The fire is okay, I guess. But the problem is, tissue don't have stiffness or rigidness to it. The last time I touch a real flash paper was 9 years ago. And I remember quite vividly that it was indeed a piece of paper. Not tissue.

Mu question is what is the type of paper commonly used for manufacturing flash paper? Thank you.. Cheers!

It's made from blotting-paper.
But now a WARNING:
It's not simple: I have the chemicals and the paper......
Prepare it open area, away from buildings etc., use rubber gloves and ASK A CHEMIST HOW THE HANDLE THESE CHEMICALS

Thanknyou!! This is a great help. I have made flash cotton my self. And yes.. It is a very nasty process. The fumes can actually kill someone.