The proof test is the whole difference
Insulation on a rated tool is applied in layers, usually in contrasting colours so that wear through the outer layer is visible before it becomes dangerous. Every individual tool is then proof tested at 10,000V, ten times its working rating, and the margin is what makes a 1000V rating credible.
A comfort grip goes through none of this. It is not a failed insulator, it was never an insulator. The distinction matters because the two look similar on a bench and completely different in a fault.
How to tell them apart
On the tool itself, not on the packaging or the listing:
- The double triangle symbol, which means suitable for live working
- The 1000V rating, printed or moulded into the insulation
- Contrasting insulation layers, so wear shows
- The standard number, IEC 60900 or its regional equivalents
If you are holding a tool and cannot find the marking, treat it as uninsulated. A tool that has lost its marking through wear has also lost the assurance the marking represented.
When insulation stops protecting you
Insulated tools are consumables, and they fail in ordinary ways: a nick from being dropped on a hard floor, a split from being levered with, a burn, a chemical softening from solvent, or simple wear exposing the inner layer.
Any of those takes the tool out of service permanently. Insulation cannot be repaired, and tape over a nick is worse than the nick because it hides it. Inspect before every use, and make binning a damaged tool a normal thing to do rather than a decision somebody has to justify.
What insulation is not
It is not permission to work live. Under the Electricity at Work Regulations, live working is the exception that has to be justified, not the default, and an insulated tool does not supply that justification.
Insulation is the last line of defence for the moment something goes wrong after you have isolated, proved dead and controlled the area. Treating it as the first line is how workshops end up relying on a £40 screwdriver to do the job a procedure should have done.