There are two types of tyre sealants in the marketplace – pre-puncture and post-puncture.
The post-puncture type may be supplied with a vehicle as an alternative to a spare wheel and can be bought as an aftermarket accessory in the form of a fluid and pump or as a one-shot aerosol can. These are designed as an emergency fix, with a sealing fluid delivered through the valve that will close up most normal punctures within the tread area. Follow the instructions supplied closely.
Pre-puncture sealants are a thixotropic fluid with other materials in suspension that is delivered through the valve tube with the core removed. This fluid coats the inside of the tyre and when a penetrating object is removed from a tyre the air pressure forces the sealant into the void closing it. These sealants can be very effective but you won’t know what other damage has been done to the tyre’s casing and these sealants could mask a more severe problem. For this reason the tyre industry does not generally recommend their use.
Neither pre- nor post-puncture sealants can be considered as a permanent repair to a punctured tyre – they are simply a means to allow limited travel to a place of safety where a permanent repair can be carried out or a replacement tyre fitted.