Glass is remarkably resilient, but one unusual quality it has is that it can be vulnerable to potential damage or even explosive cracking on particularly hot days, necessitating an urgent replacement.

Why is this? Part of it is the heat of the day itself, but to understand how to stop it happening to you, it is important to know why it happens in the first place.

Why Does Glass Shatter On Hot Days? 

It is not just windscreen glass that can break on a hot day; most types of glass can suddenly crack in certain extreme conditions such as those found during heatwaves. However, it is not just the heat itself which causes the glass to shatter.

When the heat from the sun hits a windscreen, it causes the glass to expand in largely imperceptible but important ways. If it expands evenly, the glass will not be damaged, as most cars are designed with expansion tolerances in mind for hot conditions.

However, if one part of the glass is hotter than the other, as can sometimes happen when parking in partial shade, one part of the glass may be expanding whilst the other is contracting.

This places thermal stress on the glass, causing it to shatter violently once those stresses reach a certain point.

How Do You Avoid Heat-Related Windscreen Damage?

One of the most important steps you need to take is to check any chips or tiny cracks, as these act as stress points that can be exposed and further weakened. 

Any noticeable damage should be investigated by experts and repaired professionally to avoid further problems.

As well as this, it is important to avoid sudden changes in temperature if at all possible.

This means parking in the shade as much as possible, using a UV-resistant car cover if you cannot, not turning on the air conditioning suddenly and avoiding pouring cold water on a hot windscreen.