Smoking weed in a 10 by 12 foot dorm room made of cinder-block walls with exactly one window over the course of a frigid winter in Champaign, Illinois wasn’t the easiest feat. However, like many college freshmen before us, my friends and I persevered. And by that, I mean we clumsily masked the smell of weed by using a wildly conspicuous contraption called a “sploof.”
What is a sploof, you might ask? This relic of DIY stoner culture is a toilet paper roll stuffed with and capped off on one end by dryer sheets. To use it, you exhale weed smoke through the sploof, so the stinky exhaust is pushed through the nice smelling dryer sheet-filter before entering the atmosphere.
To be sure, it works better on paper than it does in practice. Filtering your exhale through a sploof prevents the room from smelling like weed outright, but it now just smells like weed and laundry. So why are dryer sheets such an integral part of the sploof, instead of just a cloth filter, or better yet, an actual air filter? And is there a way for college freshmen today to improve upon the classic sploof design?
In order to understand how sploofs work, it’s crucial to first understand the nature of the smoke being filtered through them. Exhaled marijuana smoke is made up of mostly oil-based cannabinoids and the particulate matter range in size, so it’s critical that the filter is able to trap both small and large particles.
That’s where the chemical composition of the dryer sheets becomes the most important factor. “If the filter were made up of cotton strands, then particles, particularly those smaller and intermediate sized, would tend to follow what’s called ‘laminar flow,’ and flow right around the labyrinth of fibers and out the other end, hence no filtration,” says Shane, a nuclear physicist who asked for anonymity given the deeply chill topic at hand. “In this case, filtration is caused by the smoke particles impinging on, and being captured by, the sticky fibers that make up the dryer sheets.”
“Microscopically, dryer sheets — made from polyester or fabric — look almost exactly the same, especially when bunched up,” explains Jim Mumford, a mechanical and nuclear engineer in Michigan. “Dryer sheets are also coated in positively charged ions, which are literal magnets to smoke particles, which is why dryer sheets work much better than fabric alone would — any particles (smoke, dust, etc.) that pass through will be absorbed by the sheets.”
Per Shane, when it comes to marijuana smoke specifically, the hydrophobic agents that coat the dryer sheet fibers essentially “dissolve oil-based particles that make up exhalation,” which is why you get some small amount of scent-masking at the other end. Instead of a plume of 100 percent weed exhaust exiting the sploof, you now have a combination of those cannabinoid oil-based particles that didn’t dissolve or get trapped, plus the nice-smelling particles from the dryer sheet.
If more filtration is needed, you simply increase the amount of dryer sheets stuffed into the tube. “The best way to capture particles that might slip through unfiltered is by increasing the density of fibers in the flow, at the cost of a needed pressure change in the tube,” Shane says. “This means you might have to blow pretty hard, but you’ll definitely have more efficient filtration.”
However, this is where Mumford offers a bit of caution: “Dryer sheets aren’t exactly meant to be inhaled from, so make sure you don’t confuse the order of the proceedings, so to speak. Fiberglass in the lungs doesn’t make for a good time.”
Given the painful prospect of a lungful of fiberglass, what about those fancy smoke-exhalation filters on Amazon? Trevor Makal, associate professor of chemistry at the University of Virginia’s College at Wise, explains the difference. “If the commercial product is using activated carbon, it’s likely at least somewhat effective at eliminating odors resulting from smoke,” he tells me. “In short, a porous material, such as activated carbon — as typically found in water filters, and now nearly everywhere — can capture some of the odor chemicals present in smoke.”
This is why HEPA filters often include an activated carbon layer, he adds, as it assists in removing volatile organic compounds, or VOCs. Though he didn’t speak to the chemical makeup of exhaled marijuana smoke, he noted that the “odor compounds in tobacco smoke are primarily VOCs, and the porous nature of activated carbon leads to capture of these compounds.” He does clarify, however, that this is only true if the smoke is passing through the filter. “A smoldering cigarette that is not passing through the filter will still stink up a room,” he emphasizes.
But as someone who’s done plenty of research in “porous materials for gas capture and separation,” Makal doesn’t recall seeing dryer sheets being used in any filtration studies. “Dryer sheets, while smelling nice, are constructed from layered fibers, resulting in a rather loose structure that’s likely less effective at capturing VOCs,” he says. “I can safely say, though, that they aren’t ubiquitous in the scientific literature.”
Compared to dryer sheets, then, the commercial smoke filter might be worth a try — especially if you’re smoking weed in hotel rooms or other places where dampening the smell is necessary. But for everyone else, the sploof falls into the same category as countless other pieces of DIY stoner engineering: It’s cheap, perfect to try in a pinch and the science behind it is solid but not quite airtight (literally in this case).