The present invention relates to a formulation suitable for the preparation of a highly refractive encapsulation material with good barrier properties towards water vapor for an LED, to an encapsulation material for an LED having a high refractive index and good barrier properties towards water vapor which is obtainable from said formulation and to a light emitting device (LED) comprising said encapsulation material. The formulation comprises a polymer comprising a first repeating unit U1 and a second repeating unit U2; and a surface-modified nanoparticle, wherein the surface-modified nanoparticle does not contain any zirconium dioxide.