how do these types of insulation work?

Question

it has to do with something about convection and conduction
a)cavity wall insulation
b)Loft Insulation
c)Hot water tank jacket

Answer 1

They all basically reduce conductive heat transfer by added thermal resistance. Still air is one more thermal resistance often called a "film factor".
If convection is occurring, the heat has already been lost by conduction to the surrounding air.
Most wall and some ceiling insulation batts have a paper or a foil backing. This is usually more for a vapor barrier than for radial insulation.

Answer 2

a) cavity wall reduces conduction
b) loft insulation reduces conduction
c) reduces convection

convection is hot air rising and cold air replacing it
thus stealing heat from the hot tank

loft and walls are warm one side and cold the other side
so you must increase the insulation thickness or value
to reduce conduction through the material
(air is a better insulator than brick)