A coil in the vaping world can be used to describe a many different things but we will touch more on this later. Coils come in many different shapes, sizes and specifications but can be broken down in to two main components. First being the actual coil itself is used to turn liquid to vapour, this is often spiralled metal wire, a metal mesh or in rare cases metal encased in ceramic and is used as the heating element. Lastly, the wick (also known as the wicking element) to store the liquid against the coil/s, is most likely made of cotton but could be made of silica rope, ceramic or other natural food safe fibres.
Fun fact, this is how we got our name, the wick and the wire in a coil is crucial to vaping, without them, you couldn’t vape.
Where is the coil?
Replaceable coil tanks are one of the most common ways to vape, the coil is premade with this style of vaping and needs to be completely replaced once it has been used. The most common design is a vertical spiralled wire wrapped in cotton and encased in a cylindrical stainless-steel threaded outer casing. The air is generally drawn from the bottom and heads up through the centre of the spiralled wire. Whilst this is the most common type, variations to the heating element, wick and overall look are available and common.
Replaceable pods are a one-piece coil and tank design encompassing the heating element, wick and liquid storage. These come in many shapes, sizes, connector type, colours and are rarely the same or universal. Some manufacturers offer these prefilled or unfilled, prefilled pods might be more convenient but are more expensive in the long run and tough on the environment.
Rebuildable tanks (RTA), drippers (RDA) or the hybrid dripper with a tank (RDTA) come in so many shapes and sizes that it would be impossible to generalise. They all share two elements though, the heating element, referred to as the coil and the wicking element, most likely cotton is used but each requires a very different application of the wick. We will touch more on this in a later blog post.
The heating element
This is what gives coils their main differentiating factor, its resistance. Often shown as symbols like 0.4Ω or 1.8Ω and generally in the 0.15 to 2.0 range. Below 1ohm is often referred to as sub-ohm vaping and by far the most common type in modern vaping.
What makes the coils so different to each other?The heating element can be made out of many different types of metal. The most common material used is a rarely heard of metal called Kanthal. It is one of the most common metal used for heating, you will likely have a toaster, hairdryer, heat gun or heater that uses Kanthal wire because of its stability even when glowing hot.
Next up is stainless steel, everyone has heard of this metal because of its almost infinite use cases. Most likely your cutlery, pots & pans, barbeque, food storage and many other household products are made of this metal, it is known for its ability to resist ageing whilst being incredibly easy to clean and food safe.
Nichrome is rarely found in premade coils but often found in high end and handmade coils for rebuildable devices. The reason for this is that it is hard to work with but allows for more surface area on the coils which can lead to more flavour and vapour. It can be found in many similar places to Kanthal like toasters, hairdryers, heat guns or heaters but is generally more expensive.
The design of the heating element in premade coils is most commonly a thin wire wrapped in a spiral. In modern coils, the airflow is through the middle of the spiral but in some occasions is around the sides of the spiral. Replaceable pods vary on style but most commonly is spiralled metal wire in a horizontal form factor and airflow around the sides.
The resistance rating that premade coils display is always measured in ohms and the easiest way to differentiate between different use cases. You will find that a 5-10% difference in resistance is common, a coil rated at 0.4ohm coils can often be 0.37ohm to 0.43ohm this is normal and generally doesn’t affect performance.
But how do you know which one will suit your needs?
You don’t know at first but with a rule of thumb and some experimentation you can get very close to finding one that suits you.
Prebuilt replaceable coils:
>1ohm is generally very low wattage, tight draw (MTL), the vapour is cooler, and the nicotine level can be higher.
0.6-1.0ohms is often regarded as coils for low watt usage, the vapour is slightly warmer but nicotine level can still be high. The draw can vary from tight through to loose.
0.3-0.6ohms coils are generally designed for medium wattage applications, warm or cool vapour, more overall vapour production, medium to loose draw and nicotine strength can vary.
<0.3ohm is reserved for higher wattage coils, the vapour is warmer and plenty, nicotine strength needs to be pretty low and the draw is often almost like breathing.
Rebuildable atomizer coils
Here there aren’t as many rules, you can build however you want and for whatever wattage you want. Here you will find some 0.2ohm coils can run at 40 watts and others that need 200 watts but what causes this? The metal type used, and the overall mass of the heating element made up of the number of wraps, diameter of wraps and thickness of the wire will have the biggest effects on this. Then how do we know what to build for? Trial and error mostly, vapers are often tinkerers and have tried almost every combination available. Here are some examples
In this example we will use 24 gauge (thickness of wire, lower number is thicker wire), target resistance of 0.5 ohms and an internal diameter of 2.5mm
To achieve this with the 3 most common metal types, the following is needed:
Kanthal: 6 wraps
Stainless Steel 304: 12 wraps
Nichrome 80: 8 wraps
What can we deduce from this?
Kanthal is generally slow to heat up but has little mass so a medium wattage will be used.
Stainless will have the highest mass and likely needs the highest wattage so it isn’t too slow in ramping up.
Nichrome might have more wraps than Kanthal but still heats up quicker despite that mass. You will likely find it is the most versatile but often the hardest to work with of find good quality
The technical part has arrived, most people will never need to know about this part. Ohms law says that the current passing through a resistor between two point is directly related to the voltage difference between those two points. As simply as possible, think of hose pipe, resistance is trying to clamp down on the hose to stop the flow, volts is the amount of water trying to get past and amps is the water pressure needed to overcome the pinch caused by resistance.
The wick or wicking element is incredibly important, it draws liquid to the heating element and holds it there. Without it, the juice would spit, the vapour would be too hot, and the liquid would spill all over the place. Most commonly the wick is made of some kind of cotton. Premade replaceable coils have little to no choice but cotton for rebuildable coils comes in all shapes and sizes ranging from pads to balls to strips to rope style cotton. Just be careful, a lot of cotton for beauty use is bleached and should be avoided.
Other types of wicking elements include porous ceramic, natural fibres such as rayon and the mostly unused in modern vaping, silica wick. Each of these have downsides ranging from inconsistency, short life or just poor performance.
Why was subohming such a big deal in the early days and why can’t I use most nicotine salts with it?
Originally vaping was exclusively done with coils above 1.5ohms, as people wanted to blow bigger clouds or have more flavour, manufacturers started to make coils in lower resistances. When coils got below 1ohm, the demand from the battery grows exponentially, batteries weren’t as advanced at the time, this was potentially dangerous if mistakes were made and a lot of attention was brought to this. Now that batteries are advanced, and mods are regulated there is no danger.
Most premade nicotine salt juices are above 20mg, this is very strong. So, being that subohm vaping is primarily used to produce more vapour and more flavour, the higher strength leads to more nicotine per inhale and can be quite harsh whilst also leading to the potential of too much nicotine intake. There is almost no difference between 0.95ohm and 1.0ohm but subohming is used in warnings as it covers a lot of bases for manufacturers.
What makes a coil mouth to lung or direct to lung?
Let’s start by explaining what each of these terms are, Mouth To Lung also known as MTL is a type of vaping where you draw the vapour in to your mouth and then inhale it from there. It is very similar to a traditional cigarette as the airflow is very tight and restricted to allow for the mouth draw first whilst still producing adequate vapour.
Direct To Lung also known as DTL or DL, is a much less restricted type of vaping where you inhale the vapour straight to your lungs. The tightness of the draw ranges from breathing through a straw all the way to full open mouth breathing.
As you’ve probably worked out by now, it all comes down to the airflow. Even though most tanks have adjustable airflow control, the coil still dictates the range in which the airflow can be adjusted as the heat, throat hit and juice consumption (dry hit or leaking) need to be within a range determined by the coil and your use style.
How does temp control work?
Well a lot of people believe there is a little sensor that reads the actual temperature and tells the mod to turn the wattage up or down, but it isn’t as cut and dry as that. Instead a lot of maths is used, as metal changes temperature, the resistance changes and is measured constantly to work out where the wattage output needs to be. Only certain types of metal have this quality, stainless steel and nickel are the main two but nickel is very soft and releases bad gasses above certain temperatures. Due to this, nickel is no longer commonly used and stainless is the recommended metal in modern temperature control setups. This is why it is extremely crucial to install the tank when all components are at room temperature to get a base level reading as the changes can be incredibly minor.