The increased consumption of reading materials of all sorts was one of the key features of the "social" Enlightenment. Developments in the Industrial Revolution allowed consumer goods to be produced in greater quantities at lower prices, encouraging the spread of books, pamphlets, newspapers and journals – "media of the transmission of ideas and attitudes". Commercial development likewise increased the demand for information, along with rising populations and increased urbanisation. However, demand for reading material extended outside of the realm of the commercial, and outside the realm of the upper and middle classes, as evidenced by the Bibliothèque Bleue. Literacy rates are difficult to gauge, but in France at least, the rates doubled over the course of the 18th century. Reflecting the decreasing influence of religion, the number of books about science and art published in Paris doubled from 1720 to 1780, while the number of books about religion dropped to just one-tenth of the total.