Cladding from four tower blocks in Swansea and three in Newport have now failed fire safety checks. It comes in the wake of the Grenfell Tower tragedy in London, which killed at least 80 people.
Further tests are to be undertaken urgently on cladding and insulation after all 190 samples from buildings failed combustibility tests rolled out after the Grenfell Tower fire.
Experts will look at how different varieties of cladding insulation with different types of a aluminium panels react in a fire, says the UK Government.
The large-scale tests will involve building a 30ft high demonstration wall with a complete cladding system and subjecting it to conditions which replicate "a severe fire".
The Government said the results will help landlords make decisions on any further actions they may need to take to ensure their buildings are safe.
Meanwhile the Welsh Government said that to date no aluminium composite material has been identified in any NHS Wales buildings.
Cladding tests on three tower blocks in Newport have revealed further concerns over the safety of the buildings.
Rhyl High School will be closed for the rest of the week, while cladding used on its new building is checked.
Swansea Council says cladding systems on its four high-rise block have passed 'whole-system' safety checks.