* Papier blanc: This is the most literal translation, meaning "white paper." It's the most common and general way to say "plain paper."
* Papier simple: This means "simple paper" and is another good option.
* Papier neutre: This means "neutral paper" and is used when you want to emphasize that the paper has no lines or markings.
* Papier ordinaire: This means "ordinary paper" and is used to emphasize that the paper is basic and not special.
The best option for you will depend on the specific situation and what you want to emphasize.