Like insulation of each single part of the house, roof insulation ensures energy efficiency, prevents from moisture and mold and make your home warm. Furthermore it is good sound insulation and due to it's energy saving properties, it's environment-friendly.
There are a lot of products for roof insulation - EPS, mneral wool, PIR boards - all for pitch roof and flat roof. But which one to choose? First of all you should pay attantion for thermal conductivity value - the lower, the better. A different thermal conductivity value applies for each country, region, and building's wall type. To compare: EPS has great thermal insulation properties, it's water and mold resistant, but has a low resistance for high temperatures. Working with EPS goes really fast and comfortable. It's cheaper than mineral wool. Mineral wool provides high acoustic insulation and vapor permeability. It does not oxidize or shrink and it's not flammable. Working with mineral wool requires some experience. PIR boards gives the best insulation on the market, due to their properties, but they are impermeable products and more expensive than two others. Instead they are light, durable, easy to process and waterproof.
All the products are good and provide good thermal insualation, but in general EPS is used more often for insulating flat roofs and mineral wool for pitch roofs. PIR though is suitable for both types of roof.