Abstract: The present invention relates to a process of preparing a rubber-like material containing a protein immobilized therein, as well as a corresponding rubber-like material, the process comprising the steps of (a) mixing a protein, a branched polymer such as trimethylolpropane ethoxylate and a linear polymer such as poly(ethylene oxide) in an aqueous solution to form a gel, and (b) drying the gel to obtain a rubber-like material containing the protein immobilized therein, wherein the branched polymer comprises at least three polymeric branches bound to a central branching unit. The rubber-like material allows the immobilization and stabilization of a wide range of different proteins, including luminescent proteins as well as enzymes, and can particularly advantageously be used as down-converting material for light-emitting diodes (LEDs), for diagnostic applications, and in bioreactors.