Abstract: A shielding apparatus is provided for containing frozen bags of fluid and re particularly for containing frozen bags of blood components during microwave thaw. The apparatus includes a metal box for receiving a blood bag, the box having a bottom and sides. A metallic lid is provided, and a hinging device pivotally mounts the lid to the box for enclosing the blood bag therein. The lid and optionally the bottom of the box may be provided with an aperture for allowing microwaves to enter the box. Radiation absorbing strips are mounted along the edges of the apertures for absorbing E field reflections toward the blood bag. The apertures allow microwave energy to be concentrated in the more voluminous part of the blood bag while the edges of bag as well as any tubing are shielded by the metallic box. This apparatus prevents boiling of the blood in the lower volume areas of the bag.