There are several different types of insulation to choose from, so which type of insulation should you use? Well the answer to that is that is depends on where you want to put the insulation, what you want to achieve and how much you are willing to spend.
Fibreglass is the cheapest insulator available. It has been used for years in loft insulation where it is laid flat between and across the ceiling joists. It has also been used in timber frame walls but this is not something I could recommend, as there is a tendency for fibreglass to sag. This could result in a cold bridging effect at the top of your wall.
You can get fibreglass batts that can be used in the vertical space between studs. Modern day timber frame should be at least 140mm through its section and filling this with fibreglass is a viable cheap method of insulation your walls.
Mineral wool performs in a manner similar to Fibreglass except in terms of fire resistance where it is superior. Can be slightly more expensive than Fibreglass but remains competitively priced.
Expanded Polystyrene is most commonly found in full fill cavity wall construction where tiny white beads of polystyrene are blown into the cavity. Rigid sheets are also available and they perform in a manner similar to Fibreglass and Rockwool and is most commonly found in cavity wall and under floor construction except that they are prone to being easily damaged as they are a very brittle product.
Extruded Polystyrene is a more robust version of expanded Polystyrene which is also resistant to water penetration.
Polyurethane is usually sold in rigid sheets often with a foil backing. They are becoming more common even though they can be four to five times more expensive than their cheaper alternatives. The problems they had with CFC have now been rectified and CFC free products are now available. They are more commonly used in the roof where they are laid between rafters especially on the pitch of ceiling.
In terms of cost the order is usually as follows:
Fibreglass: Walls and Roof,
Mineral Wool: Walls and Roof,
Expanded Polystyrene: Walls and Roof and Ground,
Extruded Polystyrene: Walls, Roof and Ground,
Polyurethane: Wall, Roof and Ground.
The lower the U-Value you achieve the less heat you will lose from your home and by extension the lower your heating costs in the future.
Cost versus performance will always be an issue. It's up to you to decide where in the scale of things you want to be. With timber frame you will have no difficulty adding insulation to your design.
Increased insulation means lower U-values and lower heating costs. Timber frame and insulation is a love affair for the 21st century. Now how could you not love that equation?