I've only used the mattress for 10 nights, so this review is based on 'limited' experience.  This is a VERY firm mattress, but not uncomfortably so, at least for me anyway.  It replaced some terrible stock RV mattresses.  Because of other issues in my RV I would like to have purchased a 5" or 6" firm mattress, but they were not available.  If the mattress is still firm after ~100 nights, I'll change it to a five star rating !!     Bob in Grand Rapids, MI