Paper

Parchment was out of the reach of commoners and even some low nobles. Also, it was difficult to write on parchment. From the knowledge the system gave him, paper was cheap, more easy to write on and profitable.

For that he first gave some blueprints to the blacksmiths. And while they were working on the machines, Lui was busy buying a wooden shack. It would serve as his paper mill. Bill was given the task to cut the tree barks to wooden chips. Then they would be transported to the shack and beaten to a pulp. Then with the help of machines, it would undergo refining. Then it would go to the paper machine where water will be sucked out the pulp. Then after series of sucking and heating, it would be left to dry for some time. Then you get paper.

Explaining the method to people was a difficult task as Lui himself was unsure. This system was one weird thing. What would be next? Light in the night? Hhahaha.

After paying the blacksmiths extra for making the machines faster, they were able to complete it within two days. Only one day was left. The machines were quickly set up in the shack and the people he had hired began to work.