Loft insulation & pipe-lagging: Adequately insulating the loft (min 225mm) is a must for making your home more energy-efficient and eco-friendly. In principle it can be a pretty straightforward DIY job, which just involves laying insulation material between the rafters, but the nature of the most widely used materials means that it can also be a pretty unpleasant and potentially unhealthy task. Obviously all forms of loft insulation benefit the environment by cutting down heat loss and 
therefore make our homes more energy efficient, but some of the materials that are commonly used also have significant drawbacks as discussed below.
Don't forget to insulate fully around the access hatch and water tanks and use off-cuts and leftover insulating material to wrap round piping.
*Note: Efficiency of insulation material is measured in W/(m•K) or watts per metre-kelvin, which is referred to as a K value. As a temperature difference of 1 K = a temperature difference of 1 ºC, k is the rate of heat loss in watts across a 1 metre thickness of the material, per square metre of area, per degree Celsius of temperature difference between the two sides of the material. For those who prefer imperial this is the rate of heat loss in BTUs per hour across a 1 foot thickness of the material, per square foot of area, per degree Fahrenheit of temperature difference between the two sides of the material. So better insulators have lower K values.
Conventional insulation materials:
Fibreglass is very widely used and available in most DIY stores. On the positive side, fibreglass is a very good insulator and some brands are now using recycled glass. Technically it is possible to recycle and re-use fibreglass, although at the time of writing we are not aware of any recycling facilities for this material. On the negative side it requires a lot of energy to produce and the manufacturing process can result in harmful emissions of fluorides, chlorine & volatile organic compounds (VOC's). It is also non-biodegradeable and will emit toxic fumes when burnt. Equally concerning from a DIY perspective is the irritation it can cause to the skin, eyes & throat and there are some concerns (as yet unproven) that it may be carcinogenic. Fibreglass has a natural resistance to rot and is reasonably durable, but both compression and moisture ingress will reduce it's effectiveness over time.
Insulation performance (Fibreglass): K Value is 0.033 W/m.k - 0.040 W/m.k
*Note: If you do choose to lay fibreglass insulation always use a dust mask, goggles or glasses and make sure your skin is fully protected.
Mineral Wool is often also referred to as 'Rock Wool' (a leading brand) and is actually made up of a mix of recycled steel slag and basalt rock. The proportions are usually at least 75% steel slag and 25% basalt rock, but in some cases virtually 100% steel slag is used. Like fibreglass, mineral wools are recyclable and have the added advantage of being fireproof. However, they also share many of the failings of fibreglass, being non-biodegradeable, causing irritation to skin, eyes & throat, and also the potential (as yet unproven) threat of being a carcinogen. Mineral wools are very durable and have a natural resistance to rot, but again compression and moisture ingress will reduce their effectiveness over time. Mineral wools also emit toxic fumes when burnt.
Insulation performance (Mineral Wool): K Value - 0.033 W/m.k - 0.040 W/m.k
*Note: If you do choose to lay mineral wool insulation always use a dust mask, goggles or glasses and make sure your skin is fully protected.
Environmentally friendly insulation materials:
Wool is a nauturally renewable resource and an ideal insulating 
material with a similar thermal performance to mineral wool and fibreglass, but without the environmental or health concerns. It does however have one downside - it is more expensive. Wool is a natural material, is fully biodegradeable and recyclable, uses very little energy in its production into insulation batts (pads) and is naturally resistant to insects and decay. Even better, wool is completely safe to install, is sound absorbant, inherently moisture tolerant (without losing thermal efficiency) and also has the ability to soak-up and neutralise harmful toxins such as nitrogen oxide. With its hygroscopic qualities wool is particularly appropriate for timber framed buildings, but if you are prepared to pay a little extra for your insulation it will give eco-friendly, safe insulation that will last the lifetime of your home plus a range of other benefits to any loft (or indeed wall) irrespective of construction type. The only real negative (other than costing a little more) is that it does contain 15% polyester fibre to retain lift and stability and it has been argued that increased demand for wool could increase the national flock and therefore methane emissions!
Insulation performance (ThermaFleece): K Value - 0.037 W/m.k - 0.040 W/m.k
Recycled Newspaper is another great insulator with similar thermal performance to the above and strong environmental credentials. Like wool it is fully biodegradeable and recyclable (if kept dry) and the production process requires little energy to produce the batts. It is also completely safe to install and is less expensive than wool. Some users have reported problems with mould (although this does appear to be in exceptional cases) and moisture ingress is likely to reduce its thermal performance. It usually contains some additives for fire resistance and a fungicide as well as 'binders' to prevent compression.
Insulation performance (Warmcel 100): K value - 0.038 W/m.k - 0.040 W/m.k
Hemp is a third eco-friendly insulation alternative, and like both wool and recycled newspaper is a non-hazardous fibre and therefore completely safe to install. Furthermore it is fully biodegradable (you can even add it to your compost pile at the end of its useful life) and made from a renewable carbon-neutral resource. It has natural resistance to insect attack and the production process requires low levels of energy. Thermally it is equally as impressive as wool and shares some of the same hygroscopic properties. The high density of Isonat (35kg/cu.m) also gives it excellent acoustic properties. Like wool insulation batts it does contain 15% polyester fibre to retain lift and stability and also has non-reacting salt additives to provide fire resistance. Unfortunately another attribute it shares will wool insulation is that it is more expensive than conventional insulation materials.
Insulation performance (Isonat): K values - 0.039 W/m.k - 0.043 W/m.k
Flax is another eco-friendly insulation material which performs very similarly to hemp and shares most of it's attributes, although is slightly less dense than the hemp.
Insulation performance (IsoVlas): K value - 0.038 W/m.k - 0.040 W/m.k
Other environmentally friendly loft insulation alternatives you may wish to explore include; wood fibreboard, cork and strawboard.