Séverine Bellayer, University of Lille presented research into substitution of SVHC (substances of very high concern) brominated flame retardants in flexible polyurethane foams by sol-gel surface application of phosphorus – silicon compounds (see pinfa Newsletter n°91). For some combinations, with a surface coating thickness of around 100 nm, significant reductions of pHRR (peak heat release rate) and of carbon monoxide emission and UL94 self-extinguishing were achieved. Application on wood has also been tested. Mechanisms are thought to be production of a silicon – oxygen – phosphorus linked char and release of DEP (diethyl phosphonate) activing as a radical scavenger in the gas phase. Testing underway with bio-derived materials (cysteine from DNA, chitosan) has so far not given reliable results. Tests suggest that the treatment is physically but not chemically bound to the foam surface, but is not released in mechanical tests.