If you’re in the flexible packaging manufacturing space, chances are you’ve invested in a side sealing bag making machine—they’re the workhorses that turn thin films, laminates, and specialty materials into everything from grocery produce bags to snack pouches. But here’s a question I get asked at least a dozen times a week, often from new customers troubleshooting issues or vetting a machine before pulling the trigger: “What’s the humidity tolerance of a side sealing bag making machine?” Side Sealing Bag Making Machine
I get why this is such a critical question. I’ve been supplying these machines for 12 years now, and I’ve seen too many operators ignore humidity concerns only to end up with faulty bags, downtime, or thousands in wasted material. Back in my early days in this industry, I had a customer out in Florida who ran his plant at 82% relative humidity (RH) in the summer months, thinking a “good industrial machine” could handle it. He ran his standard polyethylene (PE) side sealing bags for three days before his sealing bars started corroding at an alarming rate, and his web tension control slipped so bad that half the production run had wavy, unsealed edges. He lost $12,000 in film material and 48 hours of production time, all because he skipped checking the humidity specs. That’s the kind of story that sticks with you, and it’s the reason I never sugarcoat this topic for potential clients.
First, let’s break down why humidity matters so much for these machines. A side sealing bag making machine works by feeding a continuous roll of film through a series of rollers, printing stations (if you’re adding logos or product info), and then heating its longitudinal sealing bars to fuse the two edges of the film together, plus heat-cutting the final bags to size. All of these moving and heating parts are sensitive to moisture in the air, but the impact varies depending on two big factors: the machine’s construction and the type of material you’re processing.
Let’s start with machine construction, because that’s where the humidity tolerance is defined. Not all side sealing bag machines are built the same, and the materials used to make them will dictate how well they hold up in humid environments. The core components that react most to moisture are the electrical parts, the sealing hardware, and the metal framing.
Standard, entry-level side sealing machines—often the ones marketed to small startups or hobbyist operations—are typically made with mild steel framing and uncoated electrical connectors. These machines, in my experience, have a maximum humidity tolerance of around 45-55% RH. Why? Mild steel rusts when exposed to consistent moisture, even in industrial settings. Rust builds up on the linear bearings that guide the sealing head, for example, creating friction that makes the machine’s movement jerky. That jerky movement can throw off the web tension of the film, leading to misaligned seals or bags that are cut too short or too long. The electrical connectors on these entry-level machines are usually cheap plastic with minimal sealing, so condensation from high humidity can cause short circuits in the control panel, stopping production cold. I’ve seen these types of machines fail entirely within 18 months in a plant that runs at 70% RH year-round.
Now, mid-range and industrial-grade side sealing machines—this is the line I supply to most of my clients—are built with humidity resistance in mind. We use galvanized steel or stainless steel for all high-contact metal parts, including framing, sealing bar housings, and linear rails. The control panels are sealed with industrial-grade gaskets, and all internal electrical components are potted in epoxy or housed in dust-proof, moisture-resistant enclosures. For these machines, the baseline humidity tolerance is 60-70% RH, depending on other factors like operating temperature and how often the plant is ventilated. I had a customer in Houston, where summer RH regularly hits 75%, run one of our mid-range machines for two years straight without a single humidity-related breakdown. His only caveat was that he installed a small dehumidifier near the sealing station, where the heating elements can add extra moisture to the air around the critical parts.
If you’re running an industrial side sealing machine that needs to operate in even more humid environments—like coastal areas (where salt air amplifies corrosion) or regions with consistent 75-80% RH—we offer a heavy-duty, corrosion-resistant upgrade line. These machines use 304 or 316 stainless steel for all metal parts, conformal coating on all circuit boards, and air-purged control panels that keep dry, filtered air inside to prevent condensation. The humidity tolerance for these upgraded machines tops out at around 85% RH, with proper ventilation and minimal dust exposure. We have a seafood packaging client in New Orleans that uses one of these upgraded models to make ice and seafood bags, and they run the machine 22 hours a day in an environment that’s often 80% RH. They’ve only had one minor issue in three years, which was a simple part replacement after a routine maintenance check.
But wait—humidity tolerance isn’t just about the machine itself. It’s also tied to the material you’re running through the machine, and how humidity interacts with that material, which in turn affects the machine’s performance. Let’s talk about that, because it’s a common mistake I see operators make: assuming the machine’s specs are all that matter, without accounting for the film or laminate.
Most side sealing bags are made from PE, polypropylene (PP), or laminated films of PE and aluminum foil, polyester, or other materials. Each of these materials reacts differently to humidity, and that reaction can make a well-built machine perform poorly even if it’s within its humidity tolerance range. For example, PE film is relatively hydrophobic—it doesn’t absorb much moisture—but high humidity can cause static electricity to build up on the film. Static electricity is a big problem for side sealing machines because it attracts dust, which can get caught between the sealing bars and the film, leading to weak seals. It can also throw off the optical sensors that align printed graphics on the film, resulting in misaligned designs or off-center bag cuts. If you’re running PE film in an environment over 65% RH, you might need to add a static eliminator bar near the film feed to keep those issues at bay—even if your machine is rated for 70% RH.
Laminated films, on the other hand, are more sensitive to humidity. The layers of different materials can absorb moisture at different rates, causing the film to expand or warp slightly. This warping makes it hard for the machine’s rollers to feed the film evenly, leading to inconsistent seal thickness or gaps along the side seams. I’ve seen a client try to run a potato chip bag laminate in a machine rated for 70% RH, but the laminate’s dimensional stability dropped off sharply above 62% RH, resulting in 15% of the bags having broken side seals. We adjusted their facility’s humidity to 60% with small dehumidifiers, and the defect rate dropped to less than 1%. That’s a perfect example of how the material’s interaction with humidity can override the machine’s specs—so it’s not enough to just ask the machine’s tolerance; you have to match that to your material.
There are also a few edge cases that push humidity tolerance beyond standard specs, and these are important to note for anyone operating in extreme conditions. For example, if you’re running a machine that’s only used for short production runs (a few hours a day, not 24/7), you might be able to get away with running it at 75% RH, even if it’s a mid-grade model. The key here is that the machine isn’t running long enough to build up significant corrosion or condensation. But if you’re running a machine 24/7, you need to stick to the lower end of its tolerance range, because the constant heat from the sealing bars and the air circulation from the motor fans will trap moisture in the components over time, leading to faster wear.
Another edge case is high temperature and humidity combined. If your plant is 90°F and 70% RH, that’s a different environment than 70°F and 70% RH. The higher temperature accelerates corrosion and causes condensation more quickly, even if the RH is the same. For that reason, we always adjust the humidity tolerance specs for operating temperature: for every 5°F above 80°F, we recommend dropping the maximum RH by 5%. So a machine rated for 70% RH at 70°F would only handle 60% RH at 90°F—something most customers don’t know, until they call us complaining that their machine is failing in their hot plant.
Now, I know what some of you are thinking: “I can just run my air conditioning to lower the humidity, right?” Well, yes, that works, but it’s not always cost-effective. If you’re running a small operation, cranking the AC 24/7 to keep humidity below 55% can add 10-15% to your monthly utility bill, which is a big hit for thin-margin packaging runs. That’s why so many clients opt for the upgraded corrosion-resistant machine, which costs a bit more upfront but saves them money on utility bills over time, especially if they’re in a consistently humid area.
The most common question I get after covering all this is: “How do I test my machine’s actual humidity performance, instead of just relying on specs?” That’s a great question, and it’s something every operator should do before ramping up production. The easiest way is to do a trial run: set your plant’s RH at different levels (using a hygrometer, which every operator should have handy) and run a small batch of your material through the machine, checking for defects like seal gaps, misaligned cuts, or sensor errors. If you’re within the machine’s rated humidity, and your material is performing well, your defect rate should be under 2% (the industry standard for high-quality bags). If defects spike, you either need to adjust the humidity, add maintenance steps, or upgrade your machine.
At the end of the day, the humidity tolerance of a side sealing bag making machine isn’t a one-number answer—it’s a range that depends on the machine’s build quality, the material you’re processing, your operating schedule, and your facility’s conditions. Over my 12 years in this business, I’ve never seen a “one-size-fits-all” spec that works for every client, which is why I always take the time to walk through each client’s specific setup before recommending a machine.
If you’re in the market for a side sealing bag making machine and want to make sure it’s the right fit for your humidity levels, or if you’re having issues with your current machine and need to troubleshoot humidity-related problems, I’m here to help. Don’t guess on specs or cut corners on testing— that’s how you end up with wasted material, downtime, and lost revenue. Reach out to my team to discuss your production needs, facility conditions, and any questions you have about humidity tolerance, and we’ll help you find the right solution for your business.
Zipper Bag Making Machine References:
- Flexible Packaging Association. (2022). Industrial Flexible Packaging Machinery Operation and Maintenance Guidelines.
- American Society of Mechanical Engineers (ASME). (2021). Humidity Effects on Industrial Manufacturing Equipment.
- International Electrotechnical Commission (IEC). (2020). Standard for Environmental Conditions for Electrical Equipment in Industrial Machinery.
Zhejiang Ruitai Packaging Machinery Co., Ltd.
Zhejiang Ruitai Packaging Machinery Co., Ltd. is one of the most professional side sealing bag making machine manufacturers and suppliers in China, featured by quality products and good service. Please rest assured to wholesale advanced side sealing bag making machine from our factory. Customized orders are welcome.
Address: D6 Building, No.66 Tingchao Road, Shangwang Town, Ruian, Zhejiang, China.
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WebSite: https://www.rtbagmachine.com/
