This is a topic that you may think is as interesting as watching paint dry, but it is important to know the difference between these two forms of insulation materials.
Traditionally, we have had fibreglass insulation in our houses in New Zealand. It is often carbon neutral in its production, due to using recycled material. However, the offcuts and any insulation pulled out down the track are not recyclable, and unfortunately can end up in landfill. Fibreglass insulation can also slump with age, so sometimes you end up with a wall only half insulated.
Polyester insulation, on the other hand, will keep its shape in the long term, ensuring your walls are kept fully insulated. The product is also generally made with recycled materials and is carbon neutral, and unlike fibreglass insulation the offcuts are recyclable as well (so long as they are responsibly removed and disposed of, i.e. not just thrown in the skip).
One myth about polyester insulation is that it is flammable, versus inflammable fibreglass insulation, but this is not accurate. During testing to AS1530 standards the flammability of the brand of polyester wall insulation that Bayside Designer Homes use came back with a 0 out of 20 ignitability.
Just like fibreglass it simply melts. The performance of the product and its recyclability in our opinion provide for a superior product, and as a result, we choose to use polyester insulation in our builds.