having helped my dad install roof insulation in 100+ houses in my early uni years I was happy that the insulation I received was a good 4 inches thick. it was also not "dusty" like some of the product we had been forced to install.
The guy did a good job and I actually got him and his dad to do a few other jobs around the house as they were reasonably priced for quality work.
the insulation certainly stops the extremes of heat / cold, but does mean the upstairs rooms stay hotter in summer, and can take longer to warm up in winter.
Am thinking I need to get something to bring the air from outside into the rooms. wouldn't take much to adjust the temperature if i could do that.
Probably hasn't reduced summer electricity consumption so much, but during winter I've seen a big drop - have two Thai guys renting rooms and I joke that they think winter is anything below 28 degrees