Two observations regarding Jason's great information and experience:
1) Many of the seemingly older pennants in Rob's Packers collection appear to be made of the thinner, stiffer, material like the one I showed--including one dated 1941 and one 25th anniversary (when was the 25th anniversary of the Packers?). That seems to go against the idea that you can confidently date pennants of that material to the late 50s and early 60s as many here have suggested.
http://feltfootball.com/green-bay-packers/
2) Two versions of the green Senators pennant were made from quite different materials, one of a fairly heavy cloth with thick paint and one of a thinner, stiffer material with thinner, almost "see-through" paint. This has been the subject of much discussion among Washington collectors over the years as to the origin of the thinner version and whether it might be some kind of repro.