Insulation generally will absolutely reduce heat entering the house in Thailand and, of course, reduce heat loss in a cold country.
The ceiling loft space is responsible for something like 25% of energy loss. The more insulation used the better but watch out for something called diminishing returns.
PE Foam is probably quite good although I prefer and have installed the quilted fiberglass. The result is what it's all about. My thinking is that there is more air in the 6" thick fiberglass so it should be a better insulator. Also the aluminium foil keeps that air from moving and stops the weight of dust from eventually collapsing the fiberglass. It is a case of personal preference which to choose I think.
I found this helpful site which you might like to look at.
https://www.greenbuildingadvisor.com/green-basics/insulation-overview-2#:~:text=ABOUT INSULATION&text=The thermal barrier of a,cutting heat loss in half.
"Doubling the thickness of insulation will double the insulation’s R-value, cutting heat loss in half. Each time the insulation layer is doubled in thickness, this rule applies. The energy saved per year by doubling insulation from R-10 to R-20, however, will be considerably more than the energy saved by doubling insulation from R-20 to R-40, because of the law of diminishing returns. In some cases, like an attic, it’s worth piling on more insulation because there is plenty of room. It’s much more expensive to add that much insulation to exterior walls."