Is it possible to confine radio frequency signal?
The easiest way to do this is with a conductive box with no holes (also known as apertures). You need a box that has a skin depth larger than the RFID signals. If using low frequency RFID which runs at 120–150 kHz, for aluminum or copper, you'll need at least 1mm of material for adequate blocking.  If the RFID uses one of the faster bands, skin depth becomes less of a concern as 0.1mm would provide sufficient blocking above 1GHz.