The functionality of sofa beds encompasses both a comfortable seating option during the day and a supportive sleeping surface at night. To meet these needs effectively, they must possess a strong framework capable of supporting the sleeper's weight. Thus, it's common for sofa beds to have a firmer construction compared to regular sofas.
Additionally, sofa beds often have a metal frame that provides support for the mattress. This metal framework also adds to the firmness of the sofa bed, making it a sturdier and more dependable option.
Furthermore, due to the specialized design of sofa beds, the mattress must be foldable and sufficiently compact to fit within the sofa's frame. This frequently leads to the mattress being thinner compared to a regular one. To make up for this reduced thickness, the sofa bed's structure must be strengthened.