Variable temperature measurements (288-303°K) of the inter-lamellar spacing in conjunction with order parameters derived for the α-carbon segment of the alkyl chain of C12(EO)4in the lamellar phase show an inter-dependence of headgroup hydration and the dynamic structure of the bilayers. Different behaviors observed for samples containing less than 30% (w/w) of water compared to those at higher hydrations and are a result of either absence or presence of “bulk” water respectively for the two situations.