This product is completely safe at 425 degrees. I spoke with a Corningware representative just to confirm that, and they said there isn't really a maximum temperature in terms of home use. ... Website says 450, but also read to lower temp by 25 like any glass dish.
Can you bake in white Corningware?
All CorningWare® oven bakeware products (including metallic-banded French White® products) can be used in conventional, convection and microwave ovens as well as in the refrigerator, freezer and dishwasher.
Is it safe to put corningware in the oven?
All glass-ceramic CORNINGWARE® can be used in conventional, convection, toaster and microwave ovens, on a rangetop, under a broiler, in the refrigerator, freezer and in the dishwasher. Use only wooden, nylon or plastic utensils. Metal utensils can scratch or leave gray marks.