The most common type of loft insulation is mineral wool in a roll, rock wool or glass wool. This is inert, inorganic, non-toxic, rot-proof and fire resistant, and should be free of CFCs and HCFCs. Manufactured to BS3533:1981, it has zero ODP (ozone depleting potential) and zero GWP (global warming potential). Another alternative is loose mineral wool, which is blown into the loft and is useful when access to roll out a loft insulation quilt is difficult. However this is a specialist rather than a diy job. You can also buy mineral fibre encapsulated in a space blanket, which avoids irritation to the skin when laying.
Because of the irritant effects of mineral wool, and the relatively large amount of energy needed to produce it (embodied energy), some people may prefer to use natural “eco-friendly” products. They can be used on top of your existing mineral wool insulation. Options are listed below. More details and suppliers here.
ThermaFleece Natural Sheep Insulation
ThermaFleece natural sheep insulation is made using wool from British sheep and takes very little energy to manufacture. It is naturally breathable, non-irritant, clean and easy to use.
Natural Hemp Insulation
Hemp Insulation is made from hemp plants. Naturally breathable.
Warmcel 100 dry cellulose insulation
Cheaper than the above, and made from 100% re-cycled fire-retardant paper (treated with organic salts that meet fire performance requirements). One bag when distributed at a depth of 100mm covers 2.5 square meters. Easy to handle. No special equipment or clothing required whilst fitting.
Not exactly natural, but involving recycling, this is made from 85% recycled plastic bottles.
Using your loft for storage can be a problem if it is fully insulated. One solution is to install rigid polystyrene insulation space boards over part of the area to provide an insulated storage deck.