Molblly 10 Inch Cooling-Gel Memory Foam Twin Size Mattress - Breathable Soft Fabric Cover for Pressure Relief & Support - Bed in a Box for Cool Sleep - Perfect for Kids Rooms, Guest Beds & Small Spaces

very firm. 2 weeks in and zero breakdown in firmness. might have to order a slightly less firm mattress if this one doesnt break in. well made, once out of the box i left it in a room for 24 hours and let it off-gas, it expanded to full height and has not sagged at all. would buy this brand again in a heartbeat, but be warned that medium firm is with the emphasis on firm.