Parchment supply could not match press demand, forcing a shift to paper

Evidence

Prices had also been driven down because paper rather than parchment had now become the preferred medium of book production. This transformation was one borne of necessity, as the supply of parchment could never feed the insatiable demand of the presses. The thirty copies of the Gutenberg Bible printed on parchment required the skins of at least 5,000 calves. — Andrew Pettegree, Arthur der Weduwen, The Library- A Fragile History, 182

Categorization

• corroborated: 2 independent passages support this claim — Andrew Pettegree, Arthur der Weduwen, The Library- A Fragile History, 182