When I went to purchase foam for my rear seat/bed.  I talked with the local
foam specialist and while they had a higher mark-up for the Memory Foam,
they recommended AGAINST the Memory Foam as they said that it would
break-down sooner than other premium foam (that is:  lose it's 'memory').

My memory foam came with a 7 year warranty.
That's good enough for me.
However, the big thing for me is it's the most comfortable thing I have ever
slept on.
I can't believe I travelled all this time without out one.