Aqueous microemulsions obtained from a perfluorinated alkane sulphonic or carboxylic acid or salt thereof, a liquid fluorinated monomer comprising a cure-site and optionally an inert liquid and highly fluorinated hydrocarbon compound. The aqueous microemulsion may be formed by mixing together water, a perfluorinated alkane sulphonic or carboxylic acid or salt thereof, optionally an inert liquid and highly fluorinated hydrocarbon compound and a liquid fluorinated monomer having a cure-site.