It's sold as 'coco-peat' here. I think it's called coconut coir there. Packed solidly - I open the top of the nest box, pile it in so it's above the edges and then pack it down and tie the lid down with cable ties so that it's pretty compacted.

Early on I used to mix in sphagnum moss and other things, but I haven't done that for years. Some of my photos have other stuff in the mix, others don't.