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Why New Cannabis Vape Cartridges Never Appear Full

April 7, 2021 in General News

The Reasons Why My Cartridge Appears Underfilled

If you are a regular cannabis vape pen user, you have most likely noticed that new vape cartridges never appear full. There is a reason for that and no, you are not being cheated by the manufacturers. The simple answer is that some of the oil has been absorbed by the wicking material of the coil. In this article, I will explain capillary action which is responsible for this occurrence. I will discuss the different types of wicking material, intake holes and the environmental forces such as temperature, pressure and humidity that influence capillary action. I will also talk about the importance of the immediate capping and sealing of the vape cartridges. Finally, I want to reassure you that due to stringent regulations, what is written on the label is exactly what is contained inside the vape cartridge.

Capillary Action

Capillary action is defined as the movement of liquid within the spaces of a porous material due to the forces of adhesion, cohesion, and surface tension. An example: Plants need capillary action to move the water and nutrients they need up into their stalks or trunks.

Coils and Wicking Material

With vaping, the cartridge filled with cannabis oil is heated using a battery which produces vapor that is inhaled. Generally, by the time you purchase a cartridge, some of the oil has already been absorbed by the coil. Due to capillary action, the wicking material absorbs the oil. This happens even when the device is not in use and continues until equilibrium is reached. The process of inhalation speeds up capillary action.

The wicking material in vape cartridges is most commonly made of porous ceramic, quartz and cotton, in which a coil of wire is wrapped around a small cotton wick. While this increases the absorption rate, it is easy to burn the wick, resulting in an unpleasant flavor and requires a replacement of the coil. This is more likely to happen when using more viscous oils or higher voltages.

Ceramic coils, with a wire wrapped around a small ceramic cylinder, are growing more popular. They offer good heat retention and are safer to use at higher voltages. Quartz coils heat up quickly but don’t retain heat as well as ceramic coils.

Intake holes

The forces of adhesion, cohesion, and surface tension are also influenced by the number and the size of the intake holes. The larger the number and the size of the intake holes, the easier it is for the coil to absorb the oil.

Storage Angle of the Cartridge

  • If the cartridge is stored vertically with the mouthpiece on top, gravity will speed up the capillary action and the absorption of the wicking material, causing the filling level to appear lower.
  • If the cartridge is stored upside down, the oil might not be in contact with the wicking material, and gravity will prevent capillary action from taking place. When the cartridge is turned upright, it takes a while for the oil to reach the coil. Please note that taking a hit before allowing enough oil to reach the coil could result in burning out the coil and possibly inhaling toxins, making it taste burnt.


Temperature affects viscosity which is why some push-button batteries have a preheat feature which is very useful in cold weather. The higher the temperature, the less viscous the oil. With exposure to heat for long periods, the coil will absorb more oil and the cartridge will look emptier. Heat exposure may also cause it to start leaking.


Submitting a vape cartridge to extreme changes in pressure at any time during the manufacturing or distribution process will impact how full the cartridge appears. Variations in pressure can negatively affect capillary action by speeding it up or slowing it down. It can also cause the cartridge to leak. In addition, adding oil to the cartridge once the wick has already absorbed a lot of oil without leaving any air in the tank will result in either the inability to vape or in leakage due to surface tension impacting capillary action.


The higher the humidity level, the more capillary action will take place, as humidity also affects cohesive and adhesive forces.

The Filling Process Impacts Capillary Action Speed

Capping and Sealing

Once the cartridge is filled, either manually or automatically, it is crucial to cap and seal it within minutes. One of the main reasons for this is to stabilize the pressure inside the cartridge, slowing the capillary action. With capping, the mouthpiece is inserted onto the filled cartridge. With sealing, a silicone cap or plug is inserted onto the mouthpiece and on the base of the cartridge for threading (510 thread).

Different Types of Extracts Affect Capillary Action

Both different types of extracts and different batches of the same extract may affect the intermolecular forces responsible for cohesion and adhesion. Without getting too technical, this explains why capillary action is unique for each extract, based on its viscosity level. For very low viscosity oils, there is typically faster absorption by the wicking material due to very high capillary action. For very high viscosity oils, there is typically  a slower absorption rate due to very low capillary action.

Critical Quality Control Points

It is important to understand that there are very strict regulations for cannabis-based products in the US regarding the labeling, the quantity and the components of the oil in cartridges. However, some manufacturers try to mask or hide the area where the cartridge does not contain oil. Be assured that with vape cartridges sold in legal cannabis states, the amount of oil printed on the label is exactly what is contained inside the cartridge.

Sources:, Why Don’t Cannabis Vaping cartridges Ever Appear Full? Arnaud Dumas De Rauly, June 12, 2020, Anatomy of A Vape Pen, Aimee O’Driscoll, May 21, 2020

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