Constraint is the best design brief there is. Give engineers infinite resources and they build something forgettable. Give them a hard legal ceiling and a deadline and you get genuinely clever hardware, which is roughly the story of the British vape market since 2025.
Here is the constraint. Under UK law, inherited from the EU Tobacco Products Directive, a vaping device cannot have a tank or pod larger than 2 millilitres. Nicotine liquid cannot be stronger than 20mg per ml, and refill containers cannot exceed 10ml. Then, in June 2025, the UK banned single-use vapes outright on environmental grounds. Whatever you sell now has to be rechargeable and refillable.
So how does a device sitting on a British shelf advertise 25,000 puffs, when 2 millilitres of liquid is worth maybe 600?
The trick: a cartridge that feeds the pod
The answer is a plumbing problem solved the way printer manufacturers solved it decades ago. Separate the part that does the work from the part that holds the supply.
The pod still holds 2ml. That is the bit with the coil in it, the bit you draw on, and it stays inside the legal definition. Clipped behind or beneath it sits a sealed 10ml container of the same liquid, which is legal in its own right as a refill container. As the pod chamber empties, liquid transfers across to top it up, driven by the pressure difference as vapour leaves the chamber. The user never opens anything, never sees a fill port, and never has 2ml of liquid become 12ml in a single vessel, which is the thing the law actually prohibits.
Stack that architecture and the numbers get silly. The Hayati Pro Ultra Plus 25000 runs a 2ml pod split into two sealed chambers, each with its own mesh coil, fed by two separate 10ml containers. Twenty-two millilitres in a device whose largest single chamber is one millilitre. Every part of it complies. Replacements ship as a single sealed unit, pod and both containers together (sold as Hayati 25K pods), because the coils and the liquid supply are designed to expire at the same time. The more modest Hayati Pro Max Plus 6000 kit uses the same idea with one chamber and one container, for 12ml.
Regulators wrote a rule about vessel size. Industry responded with a supply chain inside the product. Nobody should be surprised.
The twin-chamber problem, and how the airflow solves it
Two flavours in one device sounds easy until you think about the airway. If both coils sit under one mouthpiece and both fire, you get a blend, and not a good one. Cola and menthol do not make a third flavour, they make a mistake.
The solution is mechanical rather than electronic. The mouthpiece lifts, rotates 180 degrees and seats over one chamber at a time, physically connecting the airway to a single coil. The draw sensor then fires only the coil in that path. The other chamber sits sealed and cold, which is why the second flavour arrives clean instead of ghosted by the first, even after weeks of sitting there.
A small screen reports which side is live, usually as an L or R marker under the battery percentage. That exists because the failure mode without it is a user who has half-turned the mouthpiece, parked the airway between the two chambers and is now drawing through a restricted path, concluding their device is broken. It is the vaping equivalent of a disc tray that is nearly closed.
Mesh coils, and why the heater changed shape
Older devices used a wire coil wrapped around cotton. Heat is concentrated along the wire, which means hot spots, uneven vaporisation and the burnt note you get as wicking falls behind demand.
Mesh replaced that with a perforated metal strip. More surface area in contact with the wick, lower thermal mass per unit area, and a much faster ramp to working temperature. The practical consequences are a more consistent flavour across the life of the coil and better tolerance of the short, frequent draws that mouth-to-lung users actually take. It also tolerates the auto-feed arrangement better, because a mesh strip rewicks faster than a wrapped coil between puffs.
Resistance figures are where the sector gets sloppy. Plenty of retail listings quote 1.0 or 1.2 ohm for devices where the manufacturer publishes no resistance at all. Those numbers are invented, copied and re-copied until they look like consensus. If a spec cannot be traced to the manufacturer or the packaging, treat it as folklore.
About that 25,000
Puff ratings are lab figures, generated by a machine taking consistent, short, regular draws under controlled conditions, in the same spirit as the fuel economy figure on a car or the battery life claim on a laptop. They are not lies. They are also not what you will get.
A human draws longer, harder and unevenly. Pull for three seconds where the test pulls for two and the rating drops by roughly a third before you account for anything else. Which is why the only honest way to compare these devices is by millilitres, a quantity that is fixed, printed on the box and impossible to fudge. Divide price by millilitres and the marketing evaporates. Divide it by claimed puffs and you are comparing two manufacturers’ test protocols, which is not the same thing.
The specification that actually tells you something is the boring one: liquid volume, nicotine strength, battery capacity, charging rate. The Pro Ultra Plus runs an 850mAh cell over USB-C, which is unremarkable, and that is the point. Nobody needed to reinvent the battery. They needed to reinvent the liquid path.
What this means for hardware generally
There is a broader lesson here for anyone who watches regulated hardware. When a rule constrains one dimension of a product, engineering does not stop, it moves sideways into the dimension that was left unconstrained. Cap the tank and you get an external feed. Ban disposability and you get a device body built to survive fifteen cartridge changes with a screen and a charging port for eight pounds of bill of materials.
The next constraint is fiscal rather than physical. From October 2026 the UK taxes vaping liquid by volume at a flat rate, which for the first time makes millilitres the thing manufacturers optimise around. Expect the format engineering to continue, and expect the next generation of these devices to look like an answer to a tax code rather than to a chemistry problem.
Tushan Das runs Hayati Pro Club, an independent UK retailer specialising in one vape brand. The company is not affiliated with any manufacturer. Vaping products are for adults aged 18 and over only and contain nicotine, which is addictive.
