Double-decker is good. Double-layer lunch boxes are more practical, because the capacity of double-layer lunch boxes will be larger, and the capacity of single-layer lunch boxes is too small, which is more troublesome. I suggest buying a double-layer lunch box. The capacity of a single-layer lunch box and a double-layer rice is very different, but the price is very different. Moreover, the double-layer lunch box is really much more practical than the single-layer lunch box, especially for people with a large appetite.