Although this is the most comfortable mattress topper I"ve even owned, it does not measure 4 and a half inches. Maybe once it rests on the bed it'll plump up, but so far it only measures approx. 2 and a half inches. I slept like a baby for the 1st time in months.  I have had several back surgeries and this topper gave me such a comforting nights sleep. 

Pros: relieved all the pressure points in my lower back and legs.
Cons: does not measure  the 4.5 inches as advertized