This is the best purchase I have made in a long time and I shop a LOT. We have a king size bed and it is more firm than I like so I bought this mattress topper in XL twin size for my side of the bed. The first night I was asleep in seconds, and I have always had an incredibly hard time falling asleep. The last two nights were the same, I fell asleep immediately and I wake up with no aches in my back at all.
I recommend this to anyone who likes a soft bed, it will soften a firm mattress or make any mattress even better.
I also recommend getting a mattress cover so you don't have to have it cleaned as often. Because I am only using it for one side of the bed I also bought an XL mattress cover and tucked the fiber bed into it. I set it on my half of the bed and put the king mattress cover over everything. It makes the bed a little uneven but if you have a fluffy comforter it doesn't show as much.