Glass or stainless steel: which keeps your drink cold for longer?

The key factor in maintaining the temperature of a drink is thermal insulation. This means the ability to prevent heat from the environment from warming the liquid. And this is where materials make all the difference.

• Glass: a dense material, but an excellent conductor of temperature. This means that it quickly "receives" heat from the environment and transfers this heat to the liquid inside the glass. This is why cold drinks start to warm up in a matter of minutes, especially on hot days.
• Stainless steel: it's a metal, but when used in double-walled, vacuum-insulated glasses, it offers extremely high thermal efficiency. External heat simply can't get through easily. The result? The drink stays cold for hours.

Various home and laboratory tests show that:

• A stainless steel insulated glass can maintain the temperature of a cold drink for up to 6 hours or more, depending on the quality of the glass.
• An ordinary glass allows the drink to start losing its chill in 10 to 20 minutes.
• Single stainless steel glasses (without a double wall) perform similarly to glass, although a little better because they reflect some of the heat.

In other words: if it's a thermal stainless steel glass, it wins hands down. But if it's simple stainless steel, the advantage is not so great.

Some people say that stainless steel changes the taste of the drink. This can happen with low-quality glasses or with prolonged, poorly maintained use. Glass, on the other hand, is inert and doesn't interfere with taste. So, if your priority is pure flavor and you're going to drink quickly: glass may be preferred.

• Glass: more elegant, easy to wash, but fragile.
• Thermal stainless steel: resistant, portable, ideal for travel, the gym, the beach or work. Many have a lid, which further increases temperature conservation.

If you want to keep your drink cold for long periods of time, especially outdoors, a stainless steel thermal cup is the best choice. But if it's for quick consumption and with a focus on taste, the glass cup still has its charm.