It can be safe to use small amounts of aluminum foil in a microwave oven. Microwaves cannot pass through metal but are absorbed by food. No food completely covered by aluminum foil or in a covered metal pan should be put in a microwave oven because food wouldn't be available to absorb the microwaves.t can be safe to use small amounts of aluminum foil in a microwave oven. Microwaves cannot pass through metal but are absorbed by food. No food completely covered by aluminum foil or in a covered metal pan should be put in a microwave oven because food wouldn't be available to absorb the microwaves.