Printed in PLA, Solo's lucky dice may soften in the sun if you should possibly hang them on the rear view mirror of your car. But if you have a small metal ball chain around, you can crimp it into the cutaway corner when you fold the dice closed. the "Bchain" file has corners cut away to add a ball chain and the other file is just foldable lucky dice (don't forget to make two) See the cool video from the original MMFfolding dice page. https://www.myminifactory.com/object/3d-print-simple-16mm-dice-single-and-dual-color-81859