Insulation works by slowing the movement of heat from a hot space to one that is cool. Heat moves in three ways: radiation, conduction and convection.

Radiation is heat transfer through electromagnetic light waves that we can't see. You feel radiant heat from a burning fire or from sunlight streaming into a window that strikes your body. In the winter, warm objects in your home can radiate heat directly through glass to the outdoors unless you have special Low-E glass that blocks this infrared energy.

Conduction heat transfer happens when heat moves through an object. The heat excites the molecules in a heated object and these molecules excite the ones next to them. The closer packed the molecules are in an object, the more rapid the heat transfer. A great example of conduction is a cool spoon that is placed in a hot bowl of soup. Within a few minutes the end of the spoon not immersed in the soup will be warm or hot to the touch.

Convection heat transfer happens when a fluid such as air or water gets heated by a hot object that touches the air or water. Forced air furnaces are great examples of convection heat as the air moving over the heat exchanger gets warm and then passes that warmth to objects it touches once it is in the room.

Important to take into consideration in deciding which insulation material to use.

  • Climate
  • Ease of installation
  • Durability
  • Life cycle
  • Cost
  • Toxicity
  • Flammability
  • Environmental impact

Sheep's Wool

This material usually needs to be treated with chemicals to prevent mite infestation and reduce fire risk, although some natural builders use it untreated with success. It has very low embodied energy (unless it is imported) and performs exceptionally well as an insulation material.

  • Strong, durable and easy to handle
  • Good thermal performance
  • A local, renewable resource
  • Low embodied energy (very little energy  used in the manufacturing process)
  • Reusable and recyclable
  • Naturally resistant to fire
  • Can be made resistant to fungal andinsect attack
More effective material for sound insulation than solid alternatives

  • More expensive than other insulation materials e.g. mineral wool rolls/ batts
  • holds moisture unless an apropriate vapour barrier is installed between frame and wool
  • Challenging to install due to flexible form

Flax and Hemp

Natural plant fibres that are available in batts and rolls, and typically contain borates that act as a fungicide, insecticide and fire retardant. Potato starch is added to flax as a binder. Both materials have low embodied energy and are often combined in the same product. Examples include Isonat and Flax 100.
  • Good thermal insulation and moisture absorption properties
  •  Non-toxic and non-irritant to the touch Safe and easy to install
  •  Environmentally friendly, 100% natural product
  •  Minimal processing during manufacture
  •  Renewable resource
  •  Buildings using flax insulation are comfortable, healthy and
  • fire-safe
  •  Suitable for refurbishment and new build
  •  Exclusively for use with ventilated or breathing constructions

Wood Fibre

Made from wood chips that have been compressed into boards or batts using water or natural resins as a binder. It has very low embodied energy and uses by-products from the forestry industry. Examples include: Pavatex, Thermowall and Homatherm.

  • Good thermal insulation properties
  • Obtained from a renewable resource
  • Helps to reduce condensation by absorbing and releasing moisture
  • Easy and safe to install with no irritating fibres
  • Easily recyclable
  • Sustainable, re-newable, natural resource
  • approximately double thickness is required for equivelant level of thermal insulation compared to other types i.e. mineral wool

Expanded Clay Aggregate

These are small fired clay pellets that expand at very high temperatures to become lightweight, porous and weight-bearing. They can be used in foundations as both an insulator and aggregate. They have excellent thermal insulation properties, but high embodied energy.

Straw Bale

It is a building technique that uses straw bales (or even hay bales) for walls – which can be load-bearing, or used to infill a timber frame.

  • Low Cost
  • Low embodied costs
  • Very high thermal values
  • Highly fire resistant, relative to mineral wool (though regulations still require proofing with retardant)

  • Proofing required against moisture and pest damage
  • thick walls requirred
  • degrades over time
for more information on the details of straw-bale construction visit this link:

Cellulose (loose fill)

Cellulose is sustainable as it is made from recycled newspaper, preventing it from going to landfill. It is blown into place tightly filling all voids, creating an airtight space making it very efficient with it exceeding U Value regulations. Cellulose is also available as dry loose fill, wet spray fill, stabilised, which reduces settling, and low dust cellulose.

  • Sustainable as uses recycled material
  • U values exceed building regulations 
  • Effectively insulates voids of all shapes and sizes
  • Meets part L of building regulations
  • Reusable
  • Better than carbon zero

  • Can settle over time reducing performance however by using wet spray, or stabilised cellulose this risk is reduced
  • Can be difficult to locate local installers as it is a specialist job
  • You have to wait for the wet spray to dry out fully before finishing the walls off.
  • Loose fill weighs roughly 3 times as much as fibreglass meaning that ceiling structures need to be strong enough to support this added weight

Earth Sheltering

The use of earth against building walls to increase thermal mass and to help maintain a steady indoor temperature

Forms of construction:

  • Earth berming
Earth is piled up against exterior walls and packed, sloping away from the structure. The roof may or may not be fully covered and windows may occur on one or more sides. Due to the above ground construction this method has the fewest moisture problems

  •   In-hill construction:
Structure is set into a slope or hill side. The most practical application is in a hill facing towards the equator. There is only one exposed wall.

  • Underground recessed construction:
ground is excavated and the structure is set below ground. Often includes an atrium in the middle of the structure to provide adequate light and ventilation. 

  • Increased thermal mass
  • Reduction in energy costs
  • Increased acoustic insulation
  • Low maintenance requirements
  • Potential water seepage
  • Poor indoor air quality
  • Internal condensation
  • Construction materials are often none bio-degradeable (plastics)

Warm Roof

A warm roof is the recommended, most efficient, method of insulating a roof where the insulation, usually rigid boards is placed above the deck. A vapour barrier is essential with this type of roof construction

  • Insulation avoids condensation problems
  • It keeps the heat in the building
  • The roof does not have to be ventilated
  • Insulation is not limited by the depth of the joists


Foil Insulation

Consisting of either foil attached to a backing material or alternatively two layers of foil separated by a foam/plastic bubble layer (creating an airspace to reduce convection)
Foil reduces radiation transfer by up to 97%

  • Highly effective in warm climates
  • Compact
  • Acts as a vapour barrier
  • Non toxic/ Carcinogenic components
  • Does not mould (synthetic)

  • Must be used in conjunction with other insulation methods in cold climates
  • May cause electrical safety hazards if the foil layer comes into contact with faulty wiring.

Insulated Concrete forms (ICF)

These are generally polystyrene blocks that lock together without the need for mortar. A building form, straight or curved, can be quickly built which is then filled with concrete. ICF's are a highly efficient method of insulating concrete with them exceeding U Value regulations. They have been used on a variety of projects in the UK some of which can be viewed at some images of Cheltenham house, as seen on Grand Designs, are shown to the right.

  • Makes using concrete as a material quick and easy to build and insulate
  • Strong walls
  • Mould, rot and mildew resistant meaning they have a long lifespan 
  • Meets high regulations, with a simple construction method
  • Lightweight for easy transportation
  • Compatible with timber and steel construction
  • Flexible
  • Services can be placed within the polystyrene by melting channels into it or by placing them within the concrete

  • Adding or moving doors and windows and utilities is more complex (once construction is complete)
  • Exterior foam insulation is vunerable to ground water and insects
How an ICF works

Structural Insulated Panels (S.I.P.s)

Composite building material consisting of a layer of rigid polymer foam insulation between two layers of structural board
Board can consist of:
  • Sheet metal,
  • Plywood,
  • Cement,
  • Exterior boarding

Foam can consist of:
  • Polystyrene foam
  • Extruded polystyrene foam,
  • Polyurethane foam

Combines several components of a traditional frame structure: studs; joists; insulation; vapour barrier; air barrier.
Can be used as exterior walls, roofs, flooring and in the foundation system

  • Tighter building envelope
  • Walls have a higher insulating property
  • Construction time is reduced
  • Life cycle costs are generally lower

  • Material cost is higher than other more conventional structural and insulative materials.


Available in batts (precut) and rolls
Effectiveness as insulation reduced by compression
Gaps between batts can become sites for condensation and air infiltration (requires vapour barrier)
Air infiltration is reduced by covering batts in a layer of loose fill cellulose
Fiberglass: molten glass and 20-30% recycled industrial waste
The facing (if present) is flammable although may be modified for increased fire resistance
High density fiberglass
Plastic Fiber: usually formed from recycled plastic, does not cause irritation unlike other     types but is more difficult to cut.
Flammable but is treated with a flame retardant.

Polyurethane foam

Formed from two separate components which come into contact upon application react to form an expanding foam.

Applied directly onto the wall cavities of an unfinished wall or via holes drilled into sheathing or drywall.
  • Blocks airflow by sealing leaks and gaps
  • Works as a vapour barrier
  • Is pearmeable so reduces the chance of mould growth
  • Can be used on exsisting walls without the requirement of taking them apart
  • Can be used in tight spaces
  • Provides effective acoustic insulation
  • Is fireproof
  • Cost is high compared to other conventional insulation materials
  • Most types release toxic components upon combustion
  • Environmentally unfriendly during manufacture, application and destruction
  • Health risks during application (potential temporary blindness 2-5 days if no protection is used)

Rigid boards

Rigid insulation board, that is usually faced with foil, that can be used in flat roofs, pitched roofs, cavity walls, as under floor insulation and in composite panels. It can also be combined with plasterboard to create an insulated wall panel. Rigid boards are available in different materials such as polyurethane, polyisocyanurate and  cellular glass.

The picture  shows how you can combine rigid insulation with fibreglass to create a high R value.

  • Lightweight
  • Good performance
  • Can be cut down to fit tight spaces
  • Easy to fit
  • Available in a variety of thicknesses
  • Can be combined with other insulation types

  • Can be expensive
  • Toxic pollution can be emitted during manufacture
  • Flammable