Fibreglass is the cheapest but not necessarily the greatest product on the market. Whether it falls under another name like 'earthwool', it is still a fibreglass batt.
Let me be clear now, that the products I endorse, and service I provide are QUALITY. Cost of living is an issue to a degree, so while the Cellulose Fibre I offer may not be the cheapest product, I can ensure you that you will not have to find someone to replace or reinstall new insulation in 6/7 years time.
Electricians and other trades that may need to access your ceiling do not like fibreglass because it is itchy to work around when they need to get their job done.
Many installers and I would not recommend for any job because 99% of the time there is a better product on the market and most of the time that’s
CELLULOSE FIBRE
Some installers won’t actually install batts properly and effect your insulation's efficiency.
1% gaps loses 30% of your insulation efficiency 5% gaps reduces your efficiency by 70%.
Rats love batts because it’s easy to borrow nests into them.
Often rodent damage means they need to be replaced after 5-10 years.
Is non reusable if you want to pull it out and just goes to landfill.
Is not as fire retardant as cellulose fibre.
It won’t burn, but it will melt away from the flames exposing more of your roof and structure to the danger.
Commonly fiberglass is seen to “settle” in the roof losing R value over time causing costly replacement.
The pictures below are what I found when entering a customer's ceiling I serviced. Their complaint was that this was installed 5 months earlier, and had made little difference to their home. I was able to go in and rectify the batts that were not correctly installed, then perform our 'Blow Over' service with Cellulose to ensure that all gaps were completely filled in and give them the 100% insulation effectiveness they desired.
WHAT YOU NEED TO KNOW
While they do have some acoustic benefits, they will not be as effective as a 'dense pack' product like Cellulose Fibre. Batts will not be as affective in reducing a loud sound like rain on a tin roof.
Another thing to consider is rodents and other pests. Batts are very easy for rats/mice/snakes to burrow into and nest. It is the most common problem found in ceiling insulation. Cellulose Fibre is a loose product, so rodents can not burrow into it and look elsewhere to nest.
Fibreglass batts are difficult to recycle. In theory you could remove and reinstall but in practice they almost always have rats and snakes in them. I have never seen any batts re used by professionals because the time involved in removing rodent damage to be able to reuse them is more than the cost of just dumping them in land fill and putting new ones in. Cellulose Fibre is not only made from recycled product, it can be vacuumed out and repurposed making it a completely recyclable product. It will never go to landfill.