I have seen a few comments on the web regarding covering food in the microwave. We recommend that you do for 2 reasons.
Firstly, you don’t need much water in a container when cooking vegetables. The food doesn’t need to be covered in water. If you do completely submerge the vegetables you are wasting microwave energy in heating the water not cooking the vegetables. Just put a little water in the bottom, like a few tablespoons to keep the vegetables from drying out. The vegetables nearer the top are likely to dry out if you cook for a long time. To overcome this, if you cover the container either with its lid or with a plastic microwave cover most of the moisture will be retained in the container. The result will be evenly cooked, moist vegetables cooked in the shortest time. The same goes for other moist foods. Meat joints, sauces and soups will all stay moist rather than drying out or evaporating.
Secondly, if you cover the food container it will prevent splashes. A good example is baked beans which tend to burst when overheated. They then stick to the roof and sides of the microwave, creating more cleaning. If you cover food there will be little or no cleaning of the oven required, maybe just a quick wipe over with a damp cloth. A build up of food particles will over time reduce the efficiency of the oven (each subsequent use will sap some energy as the microwaves heat those food particles stuck to the oven) and may cause premature failure of the oven if they then burn and arc in the seams of the oven cavity. Apart from which your microwave develop a smell as the food spots rot in the warm environment inside the oven.
If you do cover food in the microwave why not use a lightweight see through cover specifically designed for the microwave. It will be easily washed and you will be assured that it is safe for microwave use. We have a few types available