I've been in a few roof spaces and underfloor areas in my time.
The worst roof I've ever been in was way out in the country and I couldn't believe my eyes when I opened the manhole.
There was all this coloured wool(like you'd get from a ball of yarn), it was all cut up and it was about 2ft deep, over the entire area of the roof space!.
And you can say what you like about wool, but Good Lord does it keep the heat in. [Linked Image]