Unlike cars and homes, mattresses don’t just gradually depreciate after their first purchase—they should be assumed to have lost all true value. Out of all the mattress shopping tips we can offer you, the simplest and most valuable is this: buy a new mattress. The difference in cost may seem vast, but the advantages of new are incalculable for a buyer.

Because the primary purpose of a mattress is to provide a supportive and comfortable night’s sleep, a mattress of unknown age and history cannot be guaranteed to fulfill this basic need. Stains, smells, and pests like bed bugs can be disguised when examining a used mattress, but their effects can linger in (and invade) your home after purchase. And used mattresses from family or close friends are not much better. Even buying a mattress direct from an original owner whom you know well makes for a dangerous investment, because even the most conscientious and clean seller is sure to inflict the greatest damage on a mattress: simple wear.

Many grandmothers hold onto their bed sets for decades, but most spring or foam mattresses will lose the strength of their support after only ten years. Unless it’s being sold because of a sudden move, most used mattresses will be around that age, or even older, rendering the true purpose of the mattress useless. Even if cost is your biggest factor in choosing a mattress, buying a lower quality, new mattress will prove a better and more lasting investment than something used or inherited. The cost of a good night’s sleep cannot be measured.