A blister pack is made by the combination of two separate sheets of material where, in one of them, cavities have been formed that allow the product to “sit in” without bulging so that the other material can be sealed on top.

There are two main types of blisters used in the pharmaceutical industry: plastic-aluminium and aluminium-aluminium. The former uses thermoforming to heat the plastic in a continuous motion whilst in the latter the cavities are formed by punching the aluminium in an intermittent motion. This is a continuous motion, plastic-aluminium blister packaging machine.

The most common plastic material used in blister packing is PVC (polyvinyl chloride) The main advantages of PVC are that it is easy to form and its low cost. The main disadvantages are that it forms a poor barrier to moisture and oxygen. In pharmaceutical packaging the PVC does not contain any plasticisers so it is sometimes referred to as UPVC i.e. unplasticised PVC.

Most PVC sheets for pharmaceutical blisters are 250µ or 0.250mm in thickness. There is also PVDC(Polyvinylidene chloride)-lined PVC, often called Duplex, which is usually in the range of 250µPVC/40gsmPVDC to 250µPVC/120gsmPVDC and offers better protection against moisture. Finally, there is PVC that contains a layer of PE (polyethylene) between the PVC and PVDC, often called Triplex, and usually has 250µ PVC/25µ PE/120gsm PVDC up to 250µ PVC/25µ PE/180gsm that offers even more protection against moisture.

There are four stages in blister packing: forming, filling, sealing and cutting. Blister packs are useful for protecting products against external factors, such as humidity and contamination for extended periods of time. Opaque blisters also protect light-sensitive products against UV rays and also make the tablets / capsules invisible to children thereby avoiding the temptation to put them in their mouth should they ever get hold of one.