Schematic evolution of a PWN inside an SNR in the presence of an extended layer of high-density filaments that penetrate the PWN itself. Top left panel: Initial structure in the free expansion phase. An SNR shell is present, bounded on the inside by a reverse shock (RS), while a high-density PWN with extended high-density fingers expandings outward. Top right panel: moment of beginning reverberation, at which the PWN also reaches the reverse shock. Bottom right panel: compression of the PWN by the SNR following reverberation. The reverse shock has disappeared, and matter in the filaments now accumulates in a thin shell at the boundary between PWN and SNR. Bottom left panel: compression of the PWN at maximum, and almost all matter in the filaments has now been accumulated in the thin shell, even though some filaments might still be present in the central region (not shown in figure).