Grenfell Tower had more than one type of flammable insulation wrapped around its exterior when last month's deadly inferno took hold, it has emerged.
A section of the block bore Kingspan Kooltherm K15 panels, a combustible form of insulation, while the rest of the building was encased in Celotex RS5000 panels.
Both materials pose a fire risk and their combination is one Kingspan said it would "never recommend".
The revelation, uncovered by Channel 4 News, adds to concerns that a recent refurbishment of the building played a crucial role in accelerating the spread of the blaze.
At least 80 people are thought to have died when the 24-storey block was engulfed by flames almost one month ago.
The insulation panels would have been installed beneath rainproof cladding Reynobond PE, which has also been identified as combustible.
The Kooltherm panels have a high resistance to stopping the spread of fire, but is still classified as flammable.
Kingspan said the material had been sourced for Grenfell Tower by a third party and supplied to the contractors who led the refurbishment.
It accounted for less than 5% of the building's total insulation, a spokesman added.
The company said in a statement: "Whilst we are still seeking to establish the facts of what occurred, it appears that Kooltherm K15 has been used without our knowledge, as part of a combination for which it was not designed, and which Kingspan would never recommend.
"Kingspan is very confident that properly installed and specified our products deliver safe, reliable and energy efficient insulation solutions."
The company was said to have no involvement in the design or specification of the £8.6 million refurbishment of Grenfell Tower.
Celotex, which provided the majority of the insulation for the block, has since discontinued the sale of RS5000 for buildings taller than 18 metres.
The Metropolitan Police indicated in the weeks following the fire that the insulation examined by experts had failed every fire safety test.
Asked on Tuesday if this included Kooltherm K15, a spokesman added they would not be naming "the specific materials or manufacturers of the material tested to date".
Contractor Harley Facades, which was charged with installing the cladding system by main developer Rydon, said in a previous statement: "It would not be appropriate for us to comment on any aspect of the fire or its causes in advance of official inquiries."