Wool as a roofing material?

I was watching this video of a Romanian Permaculture project, and around 9:04, the guy uses wool as a roofing material.

The roofing process is metal fencing, canvas tarp, wool, plastic, wool and the last layer seems exposed to the open air.

I’ve been watching his videos for years, and he has never said anything bad about it.

Has anyone ever heard of this? And if it works, why does it work?