It took exactly 4 days to fluff up  I was a little impatient, but it was worth the wait! We bought a sleep number bed abt 8 yrs ago  although they guarantee them for 10 yrs, ours was sagging  uncomfortable no matter how we adjusted it. This mattress pad did the trick!  I can still feel the vibration that came through the mattress pad. Our mattress raises  lowers as well  this worked like a charm. Thanks for giving our old mattress a little extra life!!!