What separates two ways of heating
Two designs dominate, and the difference is how the liquid reaches the heating element. One wicks it through a fibrous material; the other draws it through a porous rigid one. Everything else follows from that.
The claims attached to each are more confident than the evidence supports, and the questions worth asking concern materials and documentation rather than which design is better in the abstract.
This page covers what each design does, what the failure modes are, what the material safety questions actually are, what a manufacturer should be able to document, and what a buyer can check.
⚠️ Scope. This page describes a process and what can be verified from documents. It does not describe what a product does to a person, gives no amounts, and does not replace a healthcare professional.
🔴 The two designs
The fibrous wick
An absorbent material, historically cotton or a similar fibre, drawing liquid to a metal heating coil.
The porous rigid element
A rigid porous material, generally a ceramic, through which liquid passes to reach the heat source.
What is common to both
A metal heating element, a reservoir, an airway and a mouthpiece. The wicking method is the distinguishing variable.
What the marketing suggests
That one is categorically superior. What the evidence supports is that they behave differently and both have failure modes.
What the fibrous design does
The advantage
It wicks quickly and inexpensively, and it handles a wide range of liquid viscosities.
The failure mode
Burning. If the wick is dry when heated, the material itself burns and produces degradation products.
When that happens
Low reservoir, viscous liquid, or heating faster than the wick can supply. All three are common.
What it tastes like
Immediately and unmistakably wrong. It is the one failure mode that announces itself clearly.
What the porous design does
The advantage
It does not burn in the same way, because the material is not combustible. It also tolerates higher temperatures.
The failure mode
Clogging and uneven heating. A blocked pore structure delivers unevenly and produces hot spots.
The material question
Ceramics vary enormously. What binds the material, and what it releases when heated, depends entirely on its composition.
What that means
Ceramic is a category, not a specification. Two ceramic elements can differ completely.
🔴 The materials that matter
The heating element
Metal, and which metal matters. Alloys differ in what they release at temperature and in how they corrode.
The wicking material
Fibrous or ceramic, and in both cases the composition rather than the category is the question.
The housing and airway
Plastics and metals in the vapour path. Anything the vapour touches while hot is part of the question.
The seals
Rubber or silicone components, which are frequently overlooked and which also sit in contact with the liquid.
The heavy metal question
Why it arises
Metal components at temperature, in contact with a liquid, over repeated cycles. It is a plausible route by construction.
What has been documented
Studies across the wider vaping sector have found metal content in aerosol, with results varying enormously between devices.
What that means here
The device is a plausible contributor and it is rarely tested. Certificates in this category cover the liquid, not the hardware.
What would address it
Emissions testing on the finished device with the liquid it will carry. It exists and it is uncommon.
What a manufacturer should document
The materials
A statement of what the element, wick, housing and seals are made of. It is basic and it is frequently absent.
The temperature range
What the device is designed to operate at, since materials behave differently across ranges.
Any emissions testing
Whether the device was tested with a liquid, at operating temperature, for what came out.
The regulatory position
Which framework the device falls under in the market where it is sold, and what compliance was demonstrated.
What the liquid certificate covers
The liquid
Content, and whatever contaminant panels were run, on the material before it entered a device.
What it does not cover
Anything contributed by the hardware, anything produced by heating, and anything released by the device’s own materials.
Why the distinction matters
Because a clean liquid in an undocumented device is only half a question answered, and it is the half that is easiest to answer.
What to ask for
Both. The liquid certificate and whatever exists for the hardware. The second request is unusual and reasonable.
Temperature and what it changes
At the low end
Incomplete vaporisation and a weak result. The device delivers less than it holds.
At the high end
Degradation of the liquid, and greater release from whatever the vapour path is made of. Both increase together.
Where devices sit
Frequently unstated. Many have no temperature control at all and run at whatever the element and the battery produce.
What variable control offers
The ability to stay in a lower range, which addresses both problems at once. It is the single most useful feature.
The disposable question
What they are
Sealed units containing liquid, a battery and an element, discarded when empty.
The material question
Identical, and generally with less documentation than a refillable device.
The other issue
Waste, including lithium cells in general refuse. Several jurisdictions have moved against them for that reason.
What a buyer gives up
Any ability to inspect the device, change the liquid, or control the temperature.
What the liquid contains besides the extract
Thinning agents
Substances added to reduce viscosity so the liquid wicks properly. They are ingredients and they belong on the label.
Why they matter
Because their behaviour at temperature is a separate question from the extract’s, and it has been the subject of documented concern in the wider sector.
What to look for
A full ingredient list. A liquid described only by its extract content is not fully described.
The question to ask
What the liquid contains besides the extract and any terpenes. It is a basic composition question.
Terpenes as a thinning agent
The practice
Using terpenes to adjust viscosity, which also restores aroma removed by refinement.
Whether it is disclosed
Sometimes. Where terpenes appear on the ingredient list, they are disclosed; where a product is described as pure extract with no list, they may not be.
The source question
Whether the terpenes came from the same plant material or from elsewhere. Both are legitimate and they are different things.
What the label should say
That they are present, in position by quantity. It is an ingredient like any other.
Why cartridges resist comparison
The missing content figure
Many cartridges state no milligram total at all, only a volume and sometimes a percentage without a basis. That makes the per-milligram calculation impossible.
The missing certificate
Where one exists it frequently covers the bulk liquid rather than the filled cartridge, and the batch codes do not always connect.
What that leaves a buyer
A price, a volume, and a brand. Three things that compare nothing across sellers.
The reasonable request
The content in milligrams per cartridge, and the certificate for the filled batch. Both are ordinary and both are frequently unavailable.
Refillable against pre-filled
What refillable offers
The ability to choose the liquid, inspect the hardware, control the temperature, and replace the element when it degrades.
What pre-filled offers
Convenience, and a sealed unit where the liquid and hardware were matched by someone.
The documentation difference
A refillable setup lets you obtain a certificate for the liquid independently. A pre-filled cartridge gives you whatever the seller supplies.
The cost difference
Pre-filled is generally far more expensive per milligram, where a figure exists at all to compare.
Element degradation over time
What happens
Heating elements degrade with use. Residue accumulates, the surface changes, and delivery becomes uneven.
What that produces
A progressively worse result from the same liquid, and increasing likelihood of hot spots and localised overheating.
When to replace
When the taste changes noticeably or delivery becomes inconsistent. Both are perceptible before anything visible occurs.
What people do instead
Continue using a degraded element, which is the commonest cause of a poor experience blamed on the liquid.
Storage of a cartridge
Temperature
Cool, because the liquid degrades like any extract and heat accelerates it. A cartridge left in a car is a cartridge damaged.
Orientation
Upright, generally, so the liquid sits where it should and the element stays wetted.
Light
Away from it, for the same reason as any extract in a transparent container.
What degradation looks like
Darkening of the liquid and a changed taste. Both are visible and both indicate the same thing.
The regulatory picture
What framework applies
It varies by market and by how the product is presented. Devices, liquids and the combination can fall under different rules.
What is generally required
Product safety compliance for the device, and food or other applicable rules for the liquid depending on presentation.
Where the gaps are
Emissions from the combination, which few frameworks currently address for this category specifically.
What that means practically
A compliant device and a compliant liquid do not amount to a tested combination. That gap is real and it is not the seller’s invention.
What we would want to see
On the listing
Content in milligrams, the ingredient list including any thinning agent, and the operating temperature range.
On the certificate
The filled batch, with a code that matches the cartridge, covering content and contaminants.
From the manufacturer
The materials in the vapour path, stated specifically rather than by category.
Why we mention it
Because asking is what eventually makes these things standard. It is how contaminant panels became expected.
The three questions for this format
What is in the liquid besides the extract
Thinning agents and terpenes are the usual answers, and both belong on an ingredient list that many cartridges do not carry.
How many milligrams in the cartridge
Without it there is no comparison with anything, in this format or any other. It is the figure most often missing.
What the vapour path is made of
Element, wick, housing and seals, stated specifically. Ceramic and metal are categories rather than answers.
Why these three
Because they are the ones with factual answers that a manufacturer holds, and because no certificate in this category currently supplies any of them.
Where this format sits overall
Its genuine advantages
Portability, discretion and speed. Nothing else in the category matches it on those three, which is why it exists.
Its documentation position
The weakest in the category. A liquid certificate answers half the question and no routine document answers the other half.
What that asymmetry means
Not that the format should be avoided, but that a buyer has less to go on here than anywhere else and should know it.
The reasonable posture
Prefer refillable hardware from a manufacturer that states its materials, use a liquid with a proper certificate and ingredient list, and keep the temperature low.
A short glossary
Wick
The material carrying liquid from the reservoir to the heating element, either fibrous or a rigid porous solid.
Dry burn
Heating a wick that has no liquid in it, producing degradation products from the wick material itself.
Vapour path
Every surface the heated aerosol contacts between the element and the mouthpiece, all of which is part of the materials question.
Emissions testing
Analysis of what a device actually produces at operating temperature with a given liquid, as distinct from testing the liquid alone.
Thinning agent
A substance added to reduce a liquid’s viscosity so that it wicks correctly, which is an ingredient and belongs on the label.
The five checks that apply to any product
The batch certificate
Request it with the number printed on the packaging. A general document for the product line does not cover this batch, and those differences are exactly what it should record.
Total THC
Delta-9-THC plus THCA multiplied by 0.877, because THCA becomes THC under heat and the limit applies to the sum, not to either value alone.
Price per milligram
A division, not an opinion. The only figure that makes two products comparable, whatever the format, process and pack size.
The claims
Without an authorisation number in the EU Register these are assertions, not data — and for cannabidiol that register contains no authorised entry to this day.
The seller’s details
Company name, address and contact. Without them there is also no counterparty to turn to if something turns out to be wrong.
How this connects to the rest
With contaminant panels
They cover the liquid. The hardware is a separate and generally undocumented question.
With price per milligram
Cartridges frequently state no content figure at all, which makes them impossible to compare.
With extraction
The liquid’s composition and any residual solvent question are upstream of the device entirely.
With the certificate
It describes what went in. Nothing routine describes what comes out.
What this is for in practice
On the two designs
Different failure modes rather than a hierarchy. Burning on one, clogging and hot spots on the other.
On materials
Ceramic is a category rather than a specification. Ask what the element and the vapour path are made of.
On the liquid
Request the certificate and the full ingredient list, including any thinning agent.
On temperature
Variable control at a lower setting addresses degradation and material release together.
Frequently asked questions
What is the actual difference? How liquid reaches the element: through a fibrous wick or through a rigid porous material. Everything else follows.
Which is better? Neither categorically. One can burn dry; the other can clog and heat unevenly. Both have documented failure modes.
Is ceramic safer? Ceramic is a category, not a specification. What binds a particular ceramic and what it releases at temperature depends on its composition.
What is a dry burn? Heating a wick with no liquid in it, which burns the wick material and produces degradation products. It tastes unmistakable.
Are heavy metals a concern? It is a plausible route given metal components at temperature, and studies across the wider sector have found varying results. It is rarely tested here.
Does the liquid certificate cover the device? No. It covers the liquid before it entered any hardware. The device is a separate question.
What should a manufacturer document? The materials of the element, wick, housing and seals, the operating temperature, and any emissions testing.
What else is in the liquid? Frequently a thinning agent, and often terpenes. Both are ingredients and both belong on the label.
Does temperature matter? Substantially. Higher temperatures increase both liquid degradation and release from the vapour path materials.
What about disposables? Same material questions, generally less documentation, no temperature control, and a waste problem that several jurisdictions have acted on.
What we check and what we do not
We check what can be checked from documents: official registers, declared contents, certificates of analysis, arithmetic. We test no products, rank nothing, and assert no effects.
This is the format where the documentation gap is widest. A certificate describes a liquid that was measured before it went anywhere near a heating element, and nothing routine describes what the combination of that liquid and that hardware actually produces.
The questions worth asking are therefore about materials and about emissions rather than about which wick design is superior. Both designs work, both fail in their own way, and the composition of what the vapour touches is the part nobody publishes.