Do you mean a dig box to just burrow and play in? Or one to lay eggs in? Usually you want to use material that will hold a cave structure for an egg laying box. For burrowing it might work but it still won't really hold shape. They tend to burrow under foliage and dirt in the wild. For just burrowing down to sleep I've found that a pile of fleece scraps or some fleece blankets works well. It doesn't get caught in their nails, can hold a bit of a nest shape if that's what they're after, and it's easy to wash if it gets dirty.
Do you mean a dig box to just burrow and play in? Or one to lay eggs in? Usually you want to use material that will hold a cave structure for an egg laying box. For burrowing it might work but it still won't really hold shape. They tend to burrow under foliage and dirt in the wild. For just burrowing down to sleep I've found that a pile of fleece scraps or some fleece blankets works well. It doesn't get caught in their nails, can hold a bit of a nest shape if that's what they're after, and it's easy to wash if it gets dirty.