Hi Bunny,
If your topper was sagging by 1/2" on the floor (without any weight) then it certainly sounds like it was defective and I’m glad you were able to return it for a refund.
Casper doesn’t really have enough latex inside it to legitimately be called a latex mattress although it does contain a thin 1.5" layer of synthetic Dunlop latex. You can read more about them and some of the other simplified choice mattresses in post #2 here. A forum search on Casper (you can just click the link) will also bring up much more information about them as well.
Phoenix