The 505 jeans differ from 501s in that they have around 1% elastane woven into the mostly cotton denim. This provides stretch and flexibility to the 505 that the rigid 100% cotton 501 does not have. 505s also have a lower rise and a taper through the leg compared to 501's straight leg silhouette. The 505 creates a contemporary straight jean look compared to the 501's classic straight fit.