It's emerged that senior staff in Kingspan knew of issues with the fire certificate for an insulation product it produces was misleading.
The Grenfell fire inquiry has heard the staff knew four years before the information was made public.
72 people died in the 2017 fire in a tower block in London.
The ongoing inquiry has heard Kingspan staff knew a year before the fire that information on the fire certificate on a product used on the tower was misleading.
The inquiry yesterday heard text messages sent between some senior members of staff suggested they believed the company was lying to the market about the fire performance.
The messages are between Peter Moss from Kingspan's technical team and colleague Arron Chalmers.
In one, Mr Chalmbers says the product "doesn't actually get" a class 0 fire safety certificate, ending the message with "LOL".
The exchange continues by outlining the product was marketed as having the highest fire certificate - class 0 - even though only its outer lining achieved that and the whole product received a lower rating.
The inquiry was told Kingspan sold its Kooltherm K15 insulation with fire certificate based on a 2005 test, despite changes to the product the following year.
The inquiry is continuing.