Mattress joiner kits are a great way to connect twin beds. In the mattress joiner process, you’ll get a centerpiece, known as a bed bridge, which runs the length of the bed and fills in the gap between the two mattresses. Then, you take a strap that runs around the perimeter of both beds together to create one unified mattress. The beds are then further held together with the addition of a fitted sheet (in the case of two twins together, a king-sized fitted sheet).