Toilet paper is sold as a long strip of perforated paper wrapped around a paperboard core.
Most modern toilet paper in the developed world is designed to decompose in septic tanks.
Whereas some other bathroom and facial tissues are not.

Toilet paper comes in various plies or layers of thickness.
This can be from one-ply all the way up to six-ply.
This means that it is either a single sheet or multiple sheets placed back-to-back to make it thicker, stronger and more absorbent.
If you are looking for something for your guinea pigs to chew or something for bedding that you haven’t used before.
You may be thinking of using toilet paper?
So can guinea pigs eat toilet paper?
You know the soft tissue type.
This is absolutely fine to use.
If they chew it, it wont harm them although they probably wont chew it for long once they realise it doesn’t taste so good. So they wont eat it usually only merely chew it.