Each bunk bed is offered in a twin over twin, twin over full or full over full. All bunk beds are constructed using solid Birchwood. They do not contain any MDF or particleboard. All paints and stains are tested and are 100% free of any lead substance. All bunk beds allow for adjustable height side rails to allow for a stationary 4 drawer storage unit. All side rails are one inch thick for extra strength and durability. Also each bunk bed is stackable so that they can be converted to single beds.