On the basis of two series of X-ray photographs taken by the Laboratoire de recherche des musées de France - one of works by Poussin,the other of works by contemporary French and Italian artists - it has been posible to compare supports used for paintings in the 17th century and more particularly by Poussin. The most frequent supports found throughout the 17th century, in France and Italy, are coarse or medium weave canvases. Poussin used them at the beginning of his career, but later preferred denser, more closely woven textiles with a twill or plain weave, although these were little used generally. The twill weave is practically specific to Italian paninters, or artists living in Italy. Poussin used his support, which mostly consisted of a single width and therefore had no seams, in a given orientation. This research demonstrates that Poussin paid particular attention to the technical aspects of the execution of his works.