After spending hours on assembly, the most logical next step is to take your new wall bed for a test drive. It’s open and…shut. If the bed won’t stay down after assembly, it is usually due to the absence of weight. In some models, the front panels alone are not heavy enough to keep the bed open. For this reason, general requirements are that the mattress weigh no less than 30 pounds for a full bed or 35 pounds for a queen. You were probably planning on using a mattress with this purchase anyway, and once added, it will be enough for the bed to stay open on its own.