Four months in: what I've learned running a 3D printing filament business
I started this thing in February with €1,500 and a fairly simple idea: there are a lot of people in Portugal with 3D printers, filament isn't always cheap or easy to get quickly, and maybe — maybe — there was room for someone small to carve out a corner of that market. Four months later, I've got 271 kg of filament sitting in stock, six bottles of adhesive, a cashflow of around €600, and I've already pulled €500 back out of the original investment.
But let me back up, because the "why" matters here, and it's not some abstract business plan. It started with my own printer.
I have a 3D printer. I use it. And like anyone who owns one, I buy filament — regularly. And over time I kept noticing the same frustrating thing: filament in Portugal was consistently priced somewhere between €15 and €17.50 per kilo. Every roll. Every time. For a hobby that's supposed to be accessible and affordable, the running cost of the raw material was steep enough to make you think twice before starting a big print. I'd find myself rationing rolls, hesitating over projects, all because the plastic cost more than it felt like it should.
So I did what a lot of frustrated hobbyists do — I started digging. I went looking for suppliers, comparing prices, checking quality, trying to figure out whether the prices we were all paying were actually justified or just what the market had settled on because nobody local was undercutting it. And the more I looked, the more I thought: if I can find a supplier with a genuinely good price-to-quality ratio, I could buy in volume, sell at a price that's fairer for hobbyists like me, and still make it work as a business. The whole thing started not as a "how do I make money" idea, but as a "why is this so expensive and can I do better" idea. That, I think, is why it's worked — I built the shop I wished existed when I was the one buying.
Four months later, here's where that idea stands.
Is it a runaway success? No. Am I quitting my day job? Absolutely not. But is it working, slowly and steadily, in a way that genuinely surprises me some days? Yeah. It is. And I wanted to write down where things stand, partly to keep myself honest and partly because when I was starting out I would have killed for an honest, non-hyped account of what running a small business like this actually looks like.
So here's the realistic version. No "I made six figures in my sleep" nonsense. Just the actual numbers and the actual lessons.
The numbers, plainly
Let me lay it out because numbers are the whole point of a post like this.
Initial investment: €1,500, back in February.
Current stock: 271 kg of filament, plus 6 bottles of adhesive (the stuff people use to get prints to stick to the bed).
Cashflow: around €600.
Recovered from the initial investment: €500.
So if I'm being honest with myself, where does that leave me? I've turned €1,500 into 271 kg of physical stock, six bottles of glue, €600 of working cash, and I've already clawed back a third of what I put in. The money hasn't disappeared — it's just changed shape. Most of it is now sitting on shelves as inventory, which is exactly what you want in the early phase of a business like this. You're not trying to be cash-rich at month four. You're trying to build the thing that generates cash later.
The €500 I pulled back out matters psychologically more than financially. It's proof the model works. It's proof that money goes in, product gets sold, and money comes back out. Once you've seen that loop close even once, the whole thing stops feeling like a gamble and starts feeling like a business.
What I actually sell (and where)
I sell through two channels: OLX and a website I built myself.
OLX is the workhorse. It's where most Portuguese people go when they want to buy something locally without paying international shipping or waiting two weeks for an order to clear customs. The traffic is already there, the buyers are already looking, and for a small operation it's the path of least resistance. You list, people message you, you arrange the sale. It's not glamorous but it works.
The website is the longer game. Building it myself was partly to save money and partly because I wanted something that was mine — a proper storefront, not just a profile on someone else's platform. OLX can change its rules tomorrow. My website can't. Right now it's a smaller share of sales than OLX, but it's the foundation I want to build on, because a business that depends entirely on a third-party marketplace is a business that's always one policy change away from trouble.
As for what I sell: the bulk of my stock and my sales is PLA and PETG. Those are the two workhorse materials of 3D printing — PLA because it's easy to print and great for beginners and most general projects, PETG because it's tougher and more heat-resistant for parts that need to survive the real world. If you're stocking a filament business and you only had money for two materials, those are the two you'd pick. They're the bread and butter. They're what most people are printing, most of the time.
Beyond those, I carry small quantities of the more specialized stuff: ASA (for outdoor and UV-resistant parts), PLA CF (carbon-fibre reinforced, stiffer and with a lovely matte finish), and TPU (the flexible one, for phone cases, gaskets, that kind of thing). I only have a few units of each of these, and that's deliberate. They sell more slowly, they're more of a niche, and tying up a lot of cash in slow-moving specialty stock when you're four months in would be a mistake. Better to keep the niche materials lean and let the PLA and PETG do the heavy lifting.
€0 on marketing. Not a typo.
Here's a number I'm genuinely proud of, and it's a number that's zero: I have spent exactly nothing on marketing or advertising since the day I opened. No paid OLX boosts. No Google Ads. No Instagram promotions. No influencer deals. Zero euros, zero cents.
Every single customer who has bought from me has found me organically — and as far as I can tell, mostly through Google search. People who need filament search for it, and somehow, without me paying a cent to be there, they're finding my listings and my website. That tells me something important: the demand is real and it's specific. Nobody searches "PETG black 1kg Gaia" by accident. When someone lands on my page, they already know what they want and they're ready to buy. That's the best kind of customer there is, and I haven't had to pay to reach a single one of them.
I'm not saying I'll never spend on marketing — at some point, if I want to grow faster, a bit of targeted advertising might make sense. But the fact that the business has reached 271 kg of stock, €600 of cashflow, and a third of the investment recovered without a single euro of ad spend tells me the fundamentals are sound. If it can grow on pure organic discovery, imagine what a little marketing might do later. For now, though, I like that every euro I've earned came from someone who went looking and found me, rather than someone I paid to interrupt.
Fully online, with pickup in Gaia
The whole operation is online. There's no shop, no rent, no storefront with a sign over the door — just the OLX listings, the website, and stock kept at home. Customers either get their order shipped to them, or they pick it up locally in Gaia.
This keeps overheads about as low as they can possibly be, which matters enormously in a low-margin business like this. No commercial rent eating into thin margins. No fixed costs beyond the stock itself. The local pickup option in Gaia is popular too — a lot of buyers in the Porto area would rather drive over, save the shipping cost, grab their filament and have a quick chat than wait for a courier. It's also a nice way to build a bit of trust and a bit of a relationship with repeat customers, which you don't really get when everything goes through a shipping label.
What the focus has been so far: stock and colour variety
If I had to sum up the strategy of these first four months in one sentence, it would be: build the catalogue.
When you sell filament, you quickly learn that people don't just want "PLA." They want black PLA. Or white. Or a specific shade of red that matches the project they're building. Colour matters enormously in this business, maybe more than I expected going in. Someone printing a cosplay prop or a custom gift or a matched set of parts doesn't want "close enough" — they want the exact colour, and if you don't have it, they'll go to whoever does.
So a lot of my reinvestment has gone into widening the range of colours, especially across PLA and PETG where the demand is highest. Every time a sale comes in, a good chunk of that money goes straight back into the next order — a colour I don't have yet, a restock of something that sold well, a small test batch of something I'm curious about. That's why most of the €1,500 is now sitting as 271 kg of physical stock rather than cash in the bank. I've been deliberately aggressive about turning money into inventory, because a filament shop with a thin catalogue isn't really a filament shop. It's a guy with a few rolls of plastic.
And to put that 271 kg in perspective: I started with just over 100 kg. That was the initial stock the €1,500 bought me back in February. So in four months, through nothing but reinvesting sales back into the business, the stock has more than doubled. I didn't put in any new money — I didn't need to. The growth from ~100 kg to 271 kg came entirely from the loop working: sell some, buy more, sell some, buy more. Watching the shelves fill up over four months, knowing every extra kilo was funded by the business itself rather than my wallet, is probably the most satisfying part of this whole thing.
The 6 bottles of adhesive are a small thing but a smart one — it's a natural add-on. If someone's buying filament, there's a decent chance they could use bed adhesive too. Stocking complementary products is an easy way to nudge up the average order without much extra effort or risk.
The honest difficulties
Now the part that the motivational business gurus skip.
Margins on filament are not enormous. This isn't a high-markup luxury product — it's a commodity, and buyers can compare prices easily. You make your money on volume and on service (being local, being fast, being reliable), not on huge per-unit profit. That means the path to real income is slow. You don't get rich selling filament. You build something steady, and you grind.
Cashflow is tight when you're constantly reinvesting. Every euro that comes in is tempted straight back out into more stock. The discipline is in deciding when to reinvest and when to actually take money out — which is exactly why pulling that €500 back from the initial investment felt like a milestone. It forced me to prove the business could give money back, not just swallow it.
Storage and logistics are real considerations too. 271 kg of filament takes up space. It needs to be kept dry — filament absorbs moisture from the air and that ruins print quality — so it's not just "put it on a shelf and forget it." There's a physical, practical side to this that you don't think about until you're living with boxes of plastic in your house.
And then there's the simple reality that it's a side thing competing for time and attention against everything else in life. Responding to OLX messages, packing orders, managing the website, tracking what's selling and what isn't, deciding what to order next — it adds up. It's not passive income. It's work. Enjoyable work, but work.
Where I want to take it
The foundation phase is mostly done. I've got a catalogue, two sales channels, a proven loop of money in and money out, and a third of my investment already recovered. So what's next?
More colours, still — the catalogue can always be deeper, especially in PLA and PETG. But I'm also starting to think about whether some of those specialty materials deserve a bigger bet. If the ASA or the PLA CF start moving more consistently, I'll scale them up. The flexible TPU has a small but loyal niche too. The trick is to let the data tell me where to grow, rather than guessing — I want to expand into demand that's actually there, not demand I'm hoping exists.
The website is where my head is at for the medium term. OLX is great for getting started but I don't want to be a tenant forever. Building up direct sales through my own storefront — my own brand, my own customer relationships — is how this goes from "a guy selling filament on OLX" to an actual small business with its own identity.
The realistic verdict
Four months. €1,500 in. 271 kg of stock, 6 bottles of glue, €600 of cashflow, €500 already recovered — and €0 spent on advertising to get there. It's not a fortune. It's not going to change my life overnight. But it's real, it's working, and it's growing in the right direction, entirely on organic demand.
What I've learned most is that a small business like this isn't about a big bang. It's about the loop. Money in, product out, money back, reinvest, repeat — and slowly, with each turn of that loop, the thing gets a little bigger and a little more solid. There's no shortcut and there's no magic. There's just stock, sales, patience, and the quiet satisfaction of watching something you built from €1,500 start to stand on its own legs.
I'll check back in a few months from now with updated numbers. Hopefully the stock's bigger, the catalogue's deeper, the website's pulling more weight, and I've pulled back a bit more of that initial investment. One turn of the loop at a time.