E liquid, the liquid nicotine' fuel' in pre-filled electronic cigarette cartridges, is also available in small bottles for refilling cartridges at home.  Many people prefer to recycle their old cartridges, not only to cut down on the waste and expense involved in using new, pre-filled cartridges over a long period of time, but also because bottled e liquid comes in a far wider range of flavours.

Bottled e liquid can also be used to drip directly onto an e-cigarette atomiser for use in a method known as dripping.

There are currently only a handful of e liquid manufacturers worldwide, whose stock is passed on for re-sale by suppliers. This means that as a general rule, no matter where you buy it, the majority of e liquid contains virtually the same or at least very similar ingredients.

Besides liquid nicotine, e liquid usually contains a flavouring similar to the type used to flavour food, and either food-grade PG or VG (Propylene Glycol & Vegetable Glycerine) – both of which are humectants.

E liquid is available with nicotine content in various strengths. These usually range from nicotine-free (0mg) up to 36mg per ml. Knowing which nicotine concentration you are using is particularly useful if you'd like to monitor and perhaps reduce your nicotine intake over a period of time.

Please Note:  When handling e liquid, it's important to remember that nicotine is a poison which must be treated with caution and kept well out of the reach of children and pets, preferably in a lockable container.

E liquid is available in wide range of flavours. The flavourings are necessary because nicotine and the other main ingredients in e liquid, Propylene Glycol (PG) and Vegetable Glycerine (VG or just 'Glycerine'), possess virtually no taste or smell.

E liquid flavours are often interpreted differently by different people and finding your own favourites can involve a certain amount of trial and error.  For this reason, many suppliers now offer e liquid sample packs containing a variety of flavours in small quantities.

The ever-increasing and inventive list of e liquid flavours include many different types of tobacco flavourings, mint, coffee, vanilla, almond, chocolate, clove and a host of fruity flavours such as strawberry, cherry, banana, peach, peach cobbler and more!

There are so many variables that it's difficult to reliably estimate how many mls of e liquid equates to a pack of 20 cigarettes in terms of 'puffs'.

However, as a rough guide, approximately 1 ml of e liquid provides the equivalent number of 'puffs' as a pack of 20 cigarettes. This is when using an average size electronic cigarette.