For models intended for sleeping, the mechanism defines how easily it converts and the quality of the resulting bed.
Plywood is a reliable mid-range choice. Chipboard is the most budget-friendly but also the least durable and may crack over time. 2. Transformation Mechanisms
Common in corner sofas; a platform pulls out from under the main seat.
Folds out like an instrument to provide a large, seamless sleeping surface.
Как выбрать диван: обзор типов, особенностей и ... - D4U
The frame is the "skeleton" that supports the weight and determines the sofa's lifespan.