Prophet صلى الله عليه وسلم said, “Trap knowledge, trap knowledge.” The Sahabah رضوان لله تعالى عليهم said, “How, O’ Messenger of Allah?” Prophet صلى الله عليه وسلم said, “By writing it down.” [Khatib al-Baghdadi and others, Sahih]
When the Salaf were during a class and when their paper used to run out, they used to start writing on their sleeves. When the place would run out, they would take off their shoes and write on their upper clean part. They would, then, go home bare feet on scorching sand. As soon as they would reach home, they would copy the ‘Ilm down on paper.

We have the internet and unlimited amount of virtual ink and virtual paper.  Lets use it in the name of Allah.