A method for functionalizing a crosslinked polymer bead. The encoder performs at least a trellis encoding of a data sequence using a trellis forward-error-correction code to provide an encoded sequence, which is supplied to a channel. The energy absorber preferably is made from expanded foam beads. According to the invention the body contains the sorbent free space, which volume is sufficient to place the preset amount of the gas to be sorbed in the solid phase, and is so made, that the gas to be sorbed can be brought into the body in the solid phase.