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Automated dripping devices for vapers: RDTAs, bottomfeeders, squonk mods and dripboxes
  1. Paul Truman Harrell1,2,
  2. Thomas Eissenberg3
  1. 1 Division of Community Health & Research, Department of Pediatrics, Eastern Virginia Medical School, Norfolk, Virginia, USA
  2. 2 Department of Psychiatry & Behavioral Sciences, Eastern Virginia Medical School, Norfolk, Virginia, USA
  3. 3 Department of Psychology, Center for the Study of Tobacco Products, Virginia Commonwealth University, Richmond, Virginia, USA
  1. Correspondence to Dr Paul Truman Harrell, Department of Pediatrics, Eastern Virginia Medical School, 855 W. Brambleton Ave, Norfolk, Virginia, USA; harrelpt{at}

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The standard e-cigarette involves an electric heating coil that vaporises a liquid solution consisting of propylene glycol and/or vegetable glycerin, flavourants and, frequently, nicotine. Typically, the liquid is delivered to the heating coil via saturated wicking material. However, ‘dripping’ is another method that involves the application of liquid to the coil of a direct drip atomiser or rebuildable dripping atomiser.1 2 Users report that dripping provides greater vapour yields, stronger throat hit and a better flavour.3

Dripping is not without drawbacks. Notably, the higher temperatures involved may increase toxicant yield, although an update examining more contemporary designs may be needed.1 4 Additionally, dripping is time consuming. It requires transferring liquid from a separate container to the coil.1 This process must be repeated every few puffs to avoid ‘dry puffs’, as the liquid is vaporised and the heating coil dries out. Dry puffs yield more toxicants and may be accompanied by an aversive taste.1 5 Avoiding dry puffs by adding more liquid is challenging, as too much liquid ‘floods’ the coil, preventing vapour production. Furthermore, monitoring the amount of liquid consumed sometimes was challenging.

Automated dripping devices

To circumvent the inconvenience of direct dripping, e-cigarette users and manufacturers have developed several novel technologies, referred to here as automated dripping devices (ADD). Arguably, these include rebuildable dripping tank atomisers (RDTAs). RDTAs are advertised as offering the ‘best of both worlds.’6 As shown in figure 1, this device typically includes a cotton wick inside the atomiser that reaches down into the tank below, allowing liquid to flow from the bottom through the cotton into the coil. Alternatively, users can apply liquid into the ‘drip tip’ (mouthpiece).7 Figure 2 illustrates the two different methods of liquid application on another RDTA.8 In other cases, distributors claim that the device allows for the benefits of dripping, such as enhanced flavour, but with the practicability of a tank reservoir instead of dripping a few drops of liquid at a time.9 An additional claim is that these devices often use large amounts of coil and wick, which may allow for higher temperature use without overheating due to larger amounts of liquid available.

Figure 1

This image was found on, an online image sharing community. It apparently was posted by a user of the Avocado 24, a device manufactured by Geekvape Technology.

Figure 2

This image was found on the webpage for Geekvape Technology, an organisation with offices in both China and USA. This image was located in an advertisement for the Medusa RDTA under a heading of ‘Main Features’ and a subheading of ‘Drip refill system’.

Another category of devices, sometimes referred to as ‘bottomfeeder’ or ‘squonk mods’, more clearly provides a unique experience. Here, the liquid sits in a plastic bottle at the bottom of the device and squeezing (or ‘squonking’) the bottle feeds the liquid onto the coil. One purported advantage of this design is the large bottle reservoir. Initially, these devices were manufactured by e-cigarette enthusiasts. More recently, these devices have been mass produced (see figure 3).10

Figure 3

This advertisement was found on the webpage for KangerTech, an e-cigarette brand based in China.


We know very little about dripping, RDTAs and squonk mods. However, what we do know suggests that dripping may produce more toxicant-laden aerosol than standard e-cigarettes.1 5 There is some controversy regarding the levels of toxicants produced without dry puffs and the frequency of consumption of dry puffs by users.11 12 As a result of the lack of regulations and relative novelty of the e-cigarette market, considerable ambiguity exists regarding what devices are labelled RDTAs. For example, one distributor may advertise a device as only involving a tank,13 while another distributor advertises a very similar—if not identical—device as an RDTA.14 Further research is needed to discriminate merely semantic differences in terminology from distinctions with relevant implications.

We know little about the prevalence of dripping and essentially nothing about the frequency of ADD use. A survey of high school students in Connecticut found that about a quarter of those who had ever used e-cigarettes also reported dripping.3 However, the item assessing dripping was criticised for its potential inability to discriminate between direct dripping and ADD.15 Surveillance efforts will require improved measures to allow for discrimination between different types of ‘e-cigarettes’.

There are at least two separate issues in need of further research. One involves how e-cigarette users refer to available devices. Some of this research, involving focus groups or Internet surveillance, is ongoing16 17 but is in need of further updates, particularly in relation to dripping. A second issue involves understanding whether different types of devices are distinct from one another in a way that alters health impact. For example, if ‘dripping’ devices differ dramatically in health impact from non-dripping devices, understanding the prevalence of dripping will take on greater urgency. Regardless, current measures appear inadequate due to the lack of universal and clear definitions of different e-cigarette systems. The resulting ambiguity is a challenge to research and regulatory efforts, as well as to consumers attempting to make informed decisions regarding product purchasing. Thus, there is an urgent need for further research and discussion on this topic.



  • Contributors PTH wrote the original draft. TE provided feedback and suggestions. Both authors reviewed and approved the final manuscript.

  • Funding PTH effort is supported by the National Cancer Institute of the National Institutes of Health under award number R03CA195124 and the Center for Tobacco Products of the US Food and Drug Administration. TE effort is supported by the National Institute on Drug Abuse of the National Institutes of Health under award number P50DA036105 and the Center for Tobacco Products of the Food and Drug Administration. The content is solely the responsibility of the authors and does not necessarily represent the views of the NIH or the FDA.

  • Competing interests PTH does not have any competing interests to declare. TE is a paid consultant in litigation against the tobacco industry and is named on a patent application for a device that measures the puffing behaviour of electronic cigarette users.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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