medium density overlay (MDO)(signboard).Not to be confused with MDF which is not resistant to moisture and made of sawdust. MDO is primarily an outdoor material and is completely waterproof. This wood material has a paper overlay. Perfectly smooth surface for painting or decoupaging. Edges are crisp 90% for good folds when used for decoupaging or mod podging. All joints are mitered and glued .The lid is attached with a continuous piano hinge unlike the small hinges on the boxes you find at craft stores. This hinge is not going to become loose or break.
The dimensions of the box shown are 7-1/4X4-1/2X5-3/4 tall. It is the perfect size for 4X6 recipe cards.
This is merely an example box and I am perfectly willing to construct a similar box to your preferred dimensions.
Please see the photo of my index dividers. They are optional. The price on a set of 6 is $6.00. These are cut from high pressure laminate(formica) very strong material will not bend or sag(ever).