I was amazed at how much they held.  I was planning a 2 week trip and thought I would be using the large and medium suitcases but just needed the medium and small, and still had plenty of room left over.  I did not have to even expand them--even after all the souvenirs I bought!  After my first trip they did come back with some marks on them (airplane handlers are pretty rough on luggage), but I was able to use a little cleaner on them and they looked just like new.  The best part is, I know my luggage as soon as it hits the baggage carousel.