How wearing underwear improved medieval literacy

Is there a connection believe literacy and medieval underwear? Historians believe so, since discarded rags were used to make paper needed to print books. Before the ready availability of discarded cloth, only the rich could afford to own books.

From the article "From rags to riches, or how undergarments improved medieval literacy":

“The development of literacy was certainly helped by the introduction of paper, which was made from rags,” says Dr Marco Mostert, a historian at the Centre for Medieval Studies, Utrecht University and one of the organisers of this year’s International Medieval Congress (IMC) at the University of Leeds (UK).

“These rags came from discarded clothes, which cost much less than the very expensive parchment which was previously used for books. In the 13th century, so it is thought, as more people moved into urban centres, the use of underwear increased – which caused an increase in the number of rags available for paper-making.”