SMC Tubing FAQs: Nylon, Polyurethane, PTFE, and Mold on Plastic

If you're comparing SMC nylon tubing and SMC polyurethane tubing, researching PTFE tubing, or wondering can mold grow on plastic?—you're in the right place. I've worked on the buying side of this industry for six years, and these are the questions that keep coming up during vendor visits. Some are technical. Some are financial. Most of them are connected.

What's the difference between SMC nylon tubing and SMC polyurethane tubing?

Nylon is the workhorse of the two. It handles higher working pressures, resists abrasion, and is usually the lower-cost option. Polyurethane is the flexible one: it recovers from kinks, moves well in tight spaces, and holds up in dynamic flexing applications. In a pneumatic system, I'd use SMC nylon tubing for fixed lines and SMC polyurethane tubing for moving sections or tight radius routing.

There's also a moisture factor. Nylon absorbs more water than polyurethane, which can change its dimensions and mechanical properties over time. If your line sits in a hot, humid environment, that's something to plan for. Polyurethane can cost more per meter. But if it lasts twice as long in a flexing application, the per-year cost can actually be lower. That's the difference between price and total cost—and I've spent a lot of years learning to look at the second one.

When should I choose PTFE tubing instead of nylon or polyurethane?

PTFE tubing is the specialist. It handles aggressive chemicals, resists high temperatures (continuous service around 260°C, depending on construction), and has one of the lowest friction surfaces you'll find. That's why you see it in chemical transfer, steam lines, and analytical instrumentation.

But PTFE is also softer than nylon and can cold-flow under mechanical stress. It costs more, and it's harder to get a tight bend radius without special tooling. If you're just moving clean compressed air, PTFE is probably overkill. I usually recommend it when the chemistry or temperature kills nylon and polyurethane—not before. If you do need PTFE, pay attention to wall thickness and whether the application needs a supported or heavy-wall construction.

What does “resin filler” actually mean?

“Resin filler” is one of those terms that means something slightly different depending on where you are. In sheet molding compound (SMC), resin filler usually refers to mineral fillers like calcium carbonate or alumina trihydrate added to the thermoset resin to control flow, surface finish, and flame resistance. In tubing, it often means filled PTFE or other filled compounds—glass, carbon, or bronze particles added to the resin matrix to change wear, friction, or heat transfer.

I've seen buyers treat “resin filler” as a dirty word, as if it means less material. It doesn't. Filler is what lets us tune a material for the application. The real question is whether the compound is specified correctly for your process. On a datasheet, look for the filler type and percentage, not just the polymer name.

Can mold grow on plastic?

Yes, it can. The polymer itself isn't a great food source, but plastic isn't pure polymer. Plasticizers, lubricants, organic fillers, and trapped moisture can support mold and mildew. Add warmth and still air, and you can absolutely see fungal growth on plastic surfaces—especially in dark, humid areas.

If you need to prove fungal resistance, ASTM G21 is a common test. In dry compressed-air systems, mold is less likely, but I've still seen it in condensate traps and capped lines that sat wet for months. PTFE tubing resists microbial growth better than many plastics because of its low surface energy, but it's not antimicrobial. Keep things dry, avoid stagnant water, and you'll prevent most problems.

Does food-grade tubing matter?

It matters if the tubing actually touches food or beverage. For those applications, you should look for materials that meet FDA 21 CFR or NSF/ANSI 51. That certification is a real requirement, not a marketing label.

But I've watched more than one buyer overpay for food-grade-certified tubing in an industrial air line that never gets near a product surface. That's not a bad decision if your plant has washdown zones or chemical cleaning. It's a wasted premium if it's buried in a control panel. Specify for the actual wetted contact, not for a vague sense of safety. And if a supplier can't provide the cert printed or online, assume the material doesn't have it.

How do I avoid hidden costs when sourcing SMC products?

Hidden costs are the real budget killers. In my first year, I made the classic specification error: I assumed “standard” meant the same thing to every supplier. It cost me a $600 redo when the tubing ID was off by about 0.1 mm. Learned that lesson the hard way.

Now I ask four things on every quote: unit price, tooling or setup fees, minimum order quantity, and freight terms. A low per-meter price can disappear when the MOQ pushes you to buy a year's worth of stock you don't need. I do not sign off on a PO until I've seen the total cost, not just the per-meter price. (Note to self: check the ID before approving next time.)

Are “standard” SMC tube sizes actually standard?

Not always. Tube outer diameters are fairly standard because they have to fit into fittings. But wall thickness, inner diameter, durometer, and tolerance can vary between product lines. I've compared two “6 mm” tubes from different manufacturers and found a difference of about 0.2 mm in the ID. In a low-pressure air line, that didn't matter. In a precision timing application, it would have.

If you want to avoid surprises, ask for the datasheet and a lot traceability report before you order. That's especially important for SMC nylon tubing and SMC polyurethane tubing, where “standard” can mean different things depending on the series. Check the tolerance table, not just the nominal size.

What's the best way to compare quotes for SMC products?

Build a spreadsheet. Not a napkin, not a mental shortcut—a spreadsheet. After comparing eight suppliers over three months, I found that a quote that looked 12% cheaper was actually about 7% more expensive once I added freight, minimums, and setup fees. I almost went with the cheaper option. In fact, I had two hours to decide before the quote expired, so I did. And then I spent two weeks second-guessing while waiting for samples.

The samples were fine, so it worked out. But I still built a simple cost-comparison spreadsheet after that, and now our procurement policy requires at least three quotes for anything over $1,000. The goal isn't to squeeze suppliers. It's to make sure I'm comparing the same product, with the same lead time, at the same total cost. I'd rather spend ten minutes explaining the comparison than deal with a mismatched order later.