This is TRULY the worst mattress both myself and my wife have EVER slept on, and in truth, wish we had NEVER purchased it . It dips deeply in the both sides where we sleep and there is a great big/high part in the centre, it is so bad we are scared that we may fall out. We have had it tested TWICE by men with plumb lines, you would think they were hanging wall paper not testing a mattress .For goodness sake you sleep on the damn thing for eight hours not for five minutes so how the hell can you test it with a plumb line. No, they have taken my money and now they do not care. TO EVERYONE WHO INTENDS TO PURCHASE A NEW MATTRESS, get one where you can try it for 100 nights and if you do not like it you can get your money back. This was told to me by one of the testers, and in my opinion DO NOT BUY A MAMMOTH.