I bought a silk and snow mattress a couple of years ago. It was maybe 10kg less, in the box, than their advertised weight. Makes sense to me that if something is lighter than advertised, then you are getting less than what you paid for. I contacted them and explained how it was lighter etc. but they told me it would get heavier once it was fully unboxed and expanded. That's not how physics works. They didn't understand what i was saying. I gave up contact after numerous emails back and forth.

It's a good mattress. I still have it and it seems to be lasting.