The present invention relates to thermoplastic compositions having; high dimensional stability at high temperatures. In particular it is directed to polyester compositions containing mica for use in dual-ovenable trays and clear lids for hot food containers. According to one embodiment, the present invention is directed to a polyester composition comprising a polyester containing greater than about 2 to less than about 10 weight % of a mica filler. According to another embodiment of the present invention the mica containing polyester is prepared by the addition of the mica during polymerization, using a buffer to minimize diethylene glycol formation. According to another embodiment of the present invention, the polyester composition containing greater than 2 to less than 10 weight % mica also contains an additive package of impact modifier, nucleating agent and pigment in a concentration from about 5 weight % to 20 weight of the total composition. According to another embodiment of the present invention, the polyester composition containing mica is thermoformed into a container, such as a food tray.