Insulating the rafters with blow-in products: rockwool vs cellulose

[Garald]

[This is a very brief version of my rather long post from yesterday night, where I give much more context.]

 

We have to insulate the low part of the rafters - the bit that is under 80cm ("combles perdus"). The contractor is proposing a rock-wool product:

 

https://www.rockwool.com/fr/produits-et-applications/produits/combles-et-toitures-inclinees/combles-perdus/laine-de-roche-a-souffler/jetrock-2/

 

From what I'm reading now, there's an important alternative, applied in much the same way (i.e., by blowing it in): cellulose products, with boron salts as the fire retardant.

An example:

 

https://www.jrs.eu/jrs_en/fiber-solutions/bu-technical-applications/applications/insulation-cellulose/insulation-cellulose.php

 

Questions:

0. Is blow-in insulation the way to go, in general?

1. What are the main factors for and against rock wool vs. cellulose?

2.  Is the price point really similar? My architect seems to think that cellulose is more expensive. I can't find the price of the JRS product I've just referred to, but the following websites seem to claim that cellulose-based is actually less expensive:

https://www.choisir.com/energie/articles/166828/ouate-de-cellulose-ou-laine-de-roche-quel-isolant-choisir

https://conseils-thermiques.org/contenu/ouate-de-cellulose.php

https://conseils-thermiques.org/contenu/laine-de-roche.php

 

These links already contain a comparison and some useful data, but I thought I should ask here.

 

(I am not using rock wool elsewhere.)