I don't think there are any major stains. It can still be used sufficiently. Bodum uses high-quality "borosilicate glass," which is also used in beakers for scientific experiments. This is not just ordinary heat-resistant glass; its extremely low coefficient of thermal expansion makes it resistant to sudden temperature changes and provides reliability that it won't break easily. When you actually hold it, Bodum's glass is thick and has a solid, substantial feel. As a brand that has been loved worldwide for many years, the "sense of security" as an everyday item is exceptional.