A Four Corners investigation, to be aired tonight, will reveal that some international manufacturers and their Australian suppliers sold polyethylene cladding knowing that it was highly flammable.

The report says Australia's slack and ambiguous building standards allowed the product's importation to continue.

The product was sold in Australia for several years, and was installed on medium and high-rise buildings in Australia until 2013.

More fire-resistant cladding was available, but was more expensive.

It is unknown how many buildings are affected, but a preliminary investigation in NSW identified more than 1,000 buildings that require further examination.

Four Corners will air on the ABC tonight at 8.30pm.

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