this five-container set includes 5, colorful, rectangular containers. Each piece is composed of our signature borosilicate glass complemented by a tempered glass lid. At Genicook we believe our customers deserve the utmost quality and convenience. With this in mind, each piece in this set includes a silicone vent in the lid along with a silicone sleeve. The optional vent allows for our glassware to be used safely in the oven or microwave with the lid attached. The silicone sleeve serves as a non-slip pad on any surface as well as a safe way to grab the container after heating it up.