They were printed on regular paper, not card stock, but the postal service was so gentle back then that I'm sure they arrived in good shape. I have more of these from 1903 and 1904, but Hearst made them as late as 1907. Here's the back side of the cards.
Friday, October 22, 2010
Hearst Newspapers Free Postcard Supplement
If you subscribed or bought a Hearst Sunday newspaper on December 27, 1903, you would have received this free postcard supplement. Then you could have cut them apart and mailed them off to friends and relatives telling them how much you loved the Christmas gifts they sent you.