Screens, Filters and Crutches: The Small Parts That Change Every Smoke

Three components cost almost nothing and end up in nearly every smoke. A wire or glass disc in the bowl. A rolled strip of card at the end of a joint. A carbon-packed tip sold as an upgrade to that strip of card.

All three are described as filters. Only one of them has ever been tested, and the test did not go the way anyone expected.

Do filters remove THC?

A smoking-machine study run in 1996 by MAPS and California NORML compared seven ways of smoking the same cannabis, measuring the ratio of cannabinoids to tar in the delivered smoke. One of the seven was a joint fitted with a cigarette filter.

The result: like the water pipes in the same test, the cigarette filter also performed worse than the unfiltered joint, by about 30 percent. The plain joint came out at a ratio of about 1 part cannabinoids to 13 parts tar, and the filter made that ratio worse rather than better.

The explanation the researchers offered is the key to this entire subject. Cannabinoids are exceptionally sticky and adhere to other solids. Put any surface in the path of the smoke and it collects resin, and resin is where your THC is. The filter took out cannabinoids faster than it took out tar, so a smoker has to draw more smoke to get the same effect.

That is one study, on a machine, from 1996, and nobody has repeated it. It is also the only quantitative answer anybody has.

Crutch vs. filter, and why the difference matters

The words get used interchangeably and they describe two different objects. A crutch, also called a tip or a roach, is a strip of card rolled into a hollow spiral and inserted in the mouth end of a joint. It contains no filter medium at all. It is an open tube. Its documented functions are structural: it keeps the end from collapsing, stops loose material being pulled into your mouth, and lets you smoke the joint down without burning your fingers.

A joint filter tip packed with activated carbon is a different product, with a plug of carbon granules in it, borrowed directly from the tobacco industry. Carbon does something real, and the research on what it does is worth reading carefully before paying for it.

A 2011 paper in Chemistry Central Journal explains the limit in one sentence: material in the particulate phase of smoke is generally unavailable for adsorption by filter additives. Activated carbon is a non-selective adsorbent that pulls a broad range of volatile compounds out of the gas phase. It cannot touch the particulate phase, and the particulate phase is where the tar and the cannabinoids both live.

There is one more wrinkle. The same paper notes that physical adsorption of acetaldehyde, formaldehyde and hydrogen cyanide from smoke is less effective, which is awkward, because those are the compounds carbon tips are implicitly sold against.

What cigarette filters already taught everybody

Cannabis is repeating an experiment tobacco ran for seventy years, and the results are in. A 2005 study of Japanese smokers published in Cancer Science found no reduction in lung cancer risk from charcoal filters, and smokers who switched from plain to charcoal brands showed an odds ratio of 1.7 compared to those who did not. A 2017 review in the Journal of the National Cancer Institute concluded that filter ventilation has contributed to the rise in lung adenocarcinomas among smokers, because the holes in the filter let people pull harder and take more frequent puffs while the machine recorded a lower tar number.

Stanford's tobacco research archive puts the industry's own knowledge more bluntly than any outside critic could: tobacco industry chemists were well aware that most filters removed no more tar and nicotine than would the same length of tobacco.

Read that against a rolled strip of card, which contains no filter medium whatsoever, and the conclusion is not difficult.

There is a second lesson in the tobacco story that cannabis is also repeating. Cigarette filters are made of cellulose acetate, which is a plastic, and they do not biodegrade. Around 4.5 trillion of them become litter every year, and until recently they topped the Ocean Conservancy's list of the most common items collected from beaches and waterways every year since 1986. Carbon tips and plastic-tipped pre-rolls put the same object into the same waste stream. A rolled card crutch, whatever else it does not do, is at least paper.

What a pipe screen is for

A screen is a mechanical stop. That is the whole job, and it does it well. The one peer-reviewed study of screen materials comes out of harm reduction research, not cannabis research, examining the brass and steel screens used with pipes. Its finding on materials is useful and slightly surprising: brass and stainless steel screen materials are safer to use, as they remain mostly stable during the simulated consumption process, having been heated in place with a butane lighter. Steel wool materials with the smallest wire thicknesses degrade significantly during shaping and heating, and the loose wires can be inhaled.

So the risk in a screen is not the concept. It is improvised material. A scouring pad sheds metal. A proper brass or stainless screen, under a lighter, does not.

Two honest gaps. The study was not about cannabis, though the mechanical function is identical. And there is no research at all comparing glass screens for bowl use against metal ones, so anyone claiming glass is measurably safer is stating a preference, not a finding. Glass has a real advantage that needs no study: it is inert, it is easy to see when it is dirty, and there is no alloy to wonder about.

The unexamined day is a wasted opportunity. Reflect on what you did, what you learned, and how you can improve.

John Dewey

Why a screen cannot filter smoke

Here is the arithmetic that settles the question, and it comes from two separate peer-reviewed papers.

• The brass screens examined in that harm reduction study had an aperture width of 0.28 millimeters, or 280 micrometers, in the finer mesh, and 0.52 millimeters in the coarser one.
• Cannabis smoke particles are far smaller. A 2020 study in Scientific Reports measured aged aerosol from smoked joints at an average count median diameter of 477 nanometers, which is under half a micrometer.
• That makes the hole roughly 600 to 1,000 times wider than the particle passing through it.
• Fresh smoke carries those particles at concentrations above a billion per cubic centimeter, so there is no realistic quantity for a mesh to intercept.

A screen relates to smoke the way a goalpost relates to a tennis ball. It holds back ash, ember and plant material, which is genuinely useful and is the reason it exists. It filters nothing, and was never designed to.

What changes the smoke

From the breeding side, the variables that move the numbers are all upstream of the hardware. Temperature is the big one, since a cooler burn produces fewer degradation products than a hot one. Grind size and packing density matter, because a tight pack forces a harder draw and a harder draw burns hotter. Cure matters, because badly dried flower is harsh regardless of what is in the bowl. None of those cost anything, and all of them have more effect than any screen. The last one is the flower itself. Two of ours that behave very differently in a pipe:

• Blue Cheese, an 80 percent indica at around 26 percent THC, dense and sweet, forgiving of a slightly loose pack and gentle on the throat.
• Skunk #1, the classic Afghan, Acapulco Gold and Colombian Gold hybrid at around 26 percent, sharper and earthier, and a good test of how well anything has been cured.

What the small parts are really doing

A screen holds back ash and ember, which is worth having. A crutch keeps the joint open, keeps material out of your mouth and lets you finish it, which is also worth having. Neither removes anything from the smoke, and the evidence that a carbon tip removes what people hope it removes does not exist.

The one filter ever measured on a joint made the ratio of tar to cannabinoids about 30 percent worse. That is not an argument for smoking without a tip, since a tip earns its place on structure alone. It is an argument for buying these parts for what they do instead of for what the packaging implies, and for spending the attention on temperature, grind and cure instead. Barney's Farm has been developing premium cannabis genetics since the 1980s, with over 40 Cannabis Cup wins. Explore our full seed catalog and find strains bred for every climate and skill level.