The mattress inflated instantly. However, it took 3 days of airing (ceiling fan & windows open) for the plastic smell to dissipate. We're not especially sensitive to smells, we have pets, so it was irritating to not be able to use the mattress after it inflated. We ordered 10" medium-firm because my husband's back requires more support and he needs a lower bed. He's comfortable, while I am not. For me, after a week, it's like sleeping on plywood with a mattress pad. We're going to give it more time, then reassess. I have no idea how to return an inflated mattress, but maybe we won't need to.