Not very natural for a tort that likes to burrow into the substrate. I also wonder what is in it to hold it together into a sheet? I personally wouldn't use it and would bet your tort would be happier with something it could dig into
Actually they happier after I change thier substrate using cork sheet.
I'm having troubles with natural substrates. In my country, cypress mulch is not available. They get so dirty and damaging their plastron.
In terms of digging, they only dig if they don't get enough moisture.