I allowed more than 48 hours for this mattress to take its' from.  The first time I laid down on it, I could feel my back sinking into the mattress like it was lumpy.  I only weight 186 lbs.  I then tried to flip the mattress to see if that would make any difference, but no.  There' s ripples all across the matter.  I expected a flat and medium firm mattress.  This thing is neither.