Lamellar liquid crystals of perfluoropolyether (PFPE) surfactants of relatively short chain length (average MW 450 and 730) combined with water or formamide were studied by small angle x-ray diffraction (SAXRD) for the variation of interlayer spacing as a function of solvent content. The results indicated significant solvent penetration in the fluorinated lamellae. The results give a contribution to the identification of the role played on association features by the flexibility of the PFPE chain and its large volume due to side perfluoromethyl groups.