This is Tamiya Plastic Beams 5mm Square 6 pcs White. It is a styrene resin rod that is easy to cut, fold, and even make curves by hand or heat processing. It can be glued with a plastic model adhesive, and painting is also OK for plastic models. It is also resistant to water. It can be used for various crafts together with plastic vans.
The cross section is a square with a side of 5 mm.
Tamiya Plastic Beams 5mm Square (6 pcs)