Do Glass Bottles Break When Liquids Freeze?

Why Freezing Liquids Can Crack Glass Bottles

Water expands as it freezes, increasing in volume by roughly 9 percent. Inside a rigid glass bottle, that expansion has to go somewhere. If the bottle is filled close to the brim, the pressure pushes against the walls and shoulders, and a crack can form even though the glass itself was never close to its cold limit. Ordinary soda-lime glass typically tolerates cold down to about -20°C to -40°C (-4°F to -40°F), according to one manufacturer, but water-based contents freeze at 0°C (32°F), so the contents are usually what fails first.

Which Products Are Most at Risk

Water-based products are the main concern: hydrosols and floral waters, syrups, beverages, and many sauces and lotions contain enough water to expand as they freeze. Oils tend to thicken or turn cloudy in the cold rather than expand the way water does, and alcohol-heavy formulas freeze at much lower temperatures. Exact behavior depends on the formula, so a bottle that holds up with one product may not with another. A cobalt blue glass bottle full of a water-based tonic faces a very different risk from one full of oil.

Leave Headspace Below the Neck

The simplest protection is air space. Filling a clear glass bottle to the brim leaves the contents no room to expand, while leaving space below the neck gives freezing liquid somewhere to go. How much headspace is right depends on the bottle shape, the product, and how cold it will get, so confirm it with a test before filling a full production run.

Watch for Sudden Temperature Swings

Glass can also be stressed by rapid temperature changes, such as carrying a cold bottle straight into a warm room or filling a cold bottle with a warm liquid. Letting bottles warm up gradually, and avoiding large temperature differences between a bottle and its contents, lowers that risk. Exact limits depend on the glass, so treat this as a general precaution.

How to Test Glass Bottles Before Winter Shipping

Fill a few sample bottles with your real product, leave them in the coldest place they are likely to sit, and check for cracks, leaks, and separation once they thaw. Also confirm that each cap still seals; our guide to testing a cap for a proper seal before shipping shows how. Browse our glass bottles in a range of sizes and caps to find a shape that suits your product.