If it is a loft pitched roof or simply the attic you are going to use often for example to store something then it is better to insulate the eaves themselves i e.
Pitched roof insulation types.
A range of high performance insulation products for a variety of pitched roofs including loft insulation between and over rafters and pitched roof sarking.
A new form of blown fiberglass mixes two types of glass that naturally curl.
A cold roof is the most common type there is where the insulation is laid on top of the ceiling between the joists.
Glass fibre versus rock or mineral fibre insulation.
Different types of insulation for a cold roof.
Fiberglass comes either as sheets that can be applied to the roof from the inside or as loose fibers mixed with adhesive that are blown into place.
The process of insulation depends on the roof type.
If making a warm pitched roof construction you should opt for some type of rigid insulation boards such as kingspan k7 pitched roof board or celotex xr4000 pir insulation boards which can be installed both between and over the rafters and offers a level of fire resistance if important and applicable.
The roof slopes between the rafters.
Most homes are filled with traditional fiberglass material with newer ones adopting recycled cellulose material for more environmentally friendly alternatives.
Other insulation materials include foam wool and even insulated glass for windows.