We let the mattress rise for a couple days.  It probably rose to 7.5-7.75" rather than the 8".  It had no smell when opening.  We bought it for my 3 year old daughter so I can't say whether this mattress will be able to take an average weight and keep it's shape overtime.  So far though, it is a very good mattress and my daughter is happy and comfortable with it.  I think it's a good buy for the price.