Unlike conventional cigarettes, e-cigarettes (also called vapes) do not contain tobacco, do not involve burning and thus do not produce carbon monoxide, tar or smoke. They work by heating a solution of water, flavouring, propylene glycol, and, typically, nicotine to create a vapour that the user inhales. Using an e-cigarette is often described as ‘vaping’ rather than smoking. Disposable vape pens are non-rechargeable devices that typically come ready-filled with 2ml of e-liquid (approximately 600 'puffs') and a maximum of 2% nicotine. A typical disposable vape pen, designed for single-use, contains plastic, copper and a lithium battery.