What the law says
| Glass | Minimum light that must pass through | In practice |
|---|---|---|
| Windscreen | 75% | No tint film, apart from a shade band at the top |
| Front side windows | 70% | Most factory glass is already close to the limit, so no dark tint |
| Rear side windows and rear window | No limit | Any shade, this is where tint goes |
UK rules for cars first used on or after 1 April 1985 (gov.uk, tinted vehicle windows). The police can test tint on the roadside.
Why people tint the rear windows
- Privacy for passengers and children in the back
- Anything left on the back seat or in the boot is harder to see
- Less glare and heat on sunny days
- Less UV reaching the seats and trim
- A darker, neater look from outside
After fitting
- Keep the rear windows closed for a few days while the film cures
- Small water spots or haze in the first days usually clear as it dries
- Clean tinted glass with a soft cloth and a cleaner without ammonia