Loose fill asbestos is a grey or blue grey fibrous material blown into lofts and cavities as insulation. It is the most hazardous form of asbestos found in ordinary houses because there is nothing binding it: disturbing it puts fibres straight into the air. Vermiculite, a light brown or gold granular insulation, is not asbestos itself but some of it was contaminated at source, which is why vermiculite loft insulation is sampled rather than assumed.
Loose fill asbestos
It looks like a fluffy grey or blue grey layer, sometimes under later insulation, sometimes lying loose between joists. It is friable in the fullest sense, and removal is licensable work carried out under a sealed enclosure with a clearance afterwards. If a loft has it, the loft stops being a storage space until it has been dealt with.
Vermiculite
Vermiculite is a mineral that expands into light golden granules, and it was widely used as loft insulation. It does not contain asbestos by nature, but some of the world's supply was mined alongside asbestos and carried a contamination. That is why vermiculite insulation is sampled: the answer is not visible and it changes what may be done with the loft.
What to do if you find it
Come out, close the hatch, and do not sweep, vacuum or bag anything. Ordinary vacuum cleaners spread fine fibres rather than capturing them. Get a sample taken by an accredited organisation, and if it comes back positive get quotes from HSE-licensed contractors rather than from a general builder.
Living with it
Where loose fill is undisturbed and the loft is sealed from the rooms below, management is sometimes the recommendation rather than removal. That decision belongs in a written risk assessment, and it comes with real consequences: no storage in the loft, no cabling work, and every trade told before they open the hatch.
Questions people ask about asbestos loft insulation
How do I tell the difference between cellulose and asbestos insulation?
Cellulose is shredded paper, grey and fluffy, and looks alarmingly similar to loose fill asbestos in a dark loft. The difference is not reliably visible, which is why a sample rather than a torch is the right instrument.
Is vermiculite insulation dangerous?
Vermiculite itself is not asbestos. Some batches carried contamination from the mine they came from, so it is sampled and then treated according to the result.
Can I insulate over the top of it?
Covering loose fill is not a substitute for a decision. Get it identified first, because insulating over a friable material without recording what is underneath leaves a trap for whoever opens the loft next.