If you’ve ever ordered a packaged snack in the Rocky Mountains or a medicine blister pack in La Paz, you might have noticed how some packaging feels a little puffed up compared to the same item shipped at sea level. For thermoforming film suppliers like me, this isn’t just a visual quirk—it’s a make-or-break detail when serving customers in high-altitude locations. A few years back, we got a frantic call from a food processor based in Denver: their standard polypropylene (PP) thermoforming film was blowing out of its vacuum molds during production, and they were losing 20% of their daily output to ruined parts. At first, we assumed it was a machine issue, but a quick conversation with their production manager revealed the root problem: altitude. Thermoforming Film
High-altitude areas (defined generally as 1,500 meters/4,921 feet above sea level or higher) create unique challenges for thermoforming, a manufacturing process where heated film is stretched into a mold using vacuum pressure or air pressure. The key difference here is atmospheric pressure: at higher elevations, the air pressure is significantly lower. At 3,000 meters (9,843 feet), for example, atmospheric pressure is about 70% of what it is at sea level. This might sound small, but it throws off every step of the thermoforming process—from heating the film to holding its shape during molding. So the question isn’t just “can thermoforming film be used in high altitudes” — it’s what kind of thermoforming film works, and how do you adjust both the film and process to avoid common pitfalls?
Let’s start with the basics of how thermoforming works, because the role of pressure can’t be overstated. Most rigid thermoforming (the kind used for clamshell packaging, blister packs, or trays for fresh produce) relies on vacuum forming: you clamp a sheet of film into a frame, heat it to its forming temperature, then pull the air out from underneath the mold. The higher the pressure difference between the top of the film (which is at atmospheric pressure) and the inside of the mold (which is near vacuum), the more the film stretches into the cavity. At sea level, a standard vacuum pump can pull around 28 inches of mercury (inHg) of vacuum, which creates a pressure difference of roughly 14.7 psi (pounds per square inch) — the same as atmospheric pressure at sea level. At 3,000 meters, that same vacuum pump only creates a pressure difference of about 10.3 psi, because the external atmospheric pressure is lower. That means the vacuum isn’t strong enough to pull the thin, standard film into the mold’s corners or deep cavities. That’s why our Denver customer was seeing blown-out molds without adjusting their film.
The first solution we tested for them was a thicker grade of PP film, but that backfired. Thicker film requires more heat to reach its forming temperature, and in high-altitude plants, heating elements often struggle to maintain consistent temperatures because the thinner air transfers heat faster. The thicker film stretched unevenly, creating weak spots that tore during molding. That’s when we realized: the answer isn’t just changing film thickness—it’s choosing a film engineered to perform at lower pressure differences.
So what types of thermoforming films work best in high altitudes? Let’s break down the options, based on our years of working with customers in places like Colorado, New Mexico, and parts of South America. First, polyvinyl chloride (PVC) film, long a staple for blister packaging, has good elongation properties—meaning it stretches smoothly without tearing. But we’ve found that rigid PVC can be too brittle in extreme high altitudes (over 4,000 meters/13,123 feet), where temperature fluctuations are also more extreme. At those elevations, thin PVC cracks easily during transportation, so it’s not a great pick for both forming and end-use durability.
Another option is polyester (PET) film. PET is known for its high tensile strength and heat resistance, which is a big plus when you need to warm a film enough to stretch it at altitude. But PET has lower elongation than PP, so it can struggle to fit deep mold cavities without thinning too much. For customers in moderate high altitudes (1,500 to 3,000 meters), a medium-gauge (15 to 20 mil) co-extruded PP film with a modified ethylene propylene diene monomer (EPDM) blend works well. The EPDM modification gives the film extra elasticity, so it stretches more evenly when the vacuum pressure is lower. We supply this film to a craft bakery in Boulder, Colorado, that uses it for clamshell packaging for sourdough loaves; they reported a 18% drop in mold blowouts after switching, which directly cut their production waste by almost a quarter.
But what about the biggest challenge of high-altitude thermoforming: “outgassing” or package bulging post-production? Even if you get the film to form correctly, once the packaged product is sealed, the pressure inside the package is lower than the external atmospheric pressure at altitude. That causes air to leak out or outgassed chemicals from the product to expand, making the package puff up. For pharmaceutical blister packs, this is a huge safety concern: a puffed blister is often mistaken for a defective dose, leading to returns. For food, puffed packaging can make the product look spoiled, even if it’s fine. The fix here is a thermoforming film with a lower oxygen transmission rate (OTR) — a film that acts as a barrier to keep air from moving in or out after sealing. We developed a custom film with a thin nylon inner layer for one pharmaceutical customer in La Paz, Bolivia, which sits at 3,640 meters (11,942 feet). Their blister packs used to puff 20% of the time, but after switching to our nylon-blended film, that number dropped to less than 1%.
Of course, it’s not just the film—process adjustments matter too, and that’s where our role as a supplier goes beyond just selling materials. We don’t just ship film; we work with customers to adjust their thermoforming machines for high-altitude conditions. For example, we advise increasing pre-heat time by 10 to 15% at elevations above 2,000 meters, because the lower air density means heat doesn’t transfer as evenly to the film. We also recommend using plug-assist forming—a tool that pre-stretches the film before vacuum is applied—for deep or complex molds. Plug-assist adds mechanical pressure to the film, compensating for the lower vacuum pressure at altitude, and it pairs perfectly with our modified EPDM films. A cut flower supplier in Flagstaff, Arizona, uses plug-assist forming with our films to make custom trays that keep blooms fresh during shipping to Phoenix (at 330 meters) and even as far as New York. They tell us their tray damage rate is now less than 3%, down from 12% when they used standard film.
We’ve also learned to test films in real high-altitude conditions before launching them. A few years ago, we tried to market a new bio-based thermoforming film to a customer in Cusco, Peru, at 3,400 meters. Our initial tests at our lab in Iowa showed the film had great elongation, but when we ran trials in Cusco, it tore 15% of the time. The lab didn’t account for the 20% lower relative humidity in Cusco, which makes thermoforming film more brittle. We went back to the drawing board, added a small amount of a plasticizer that’s compatible with plant-based materials, and re-tested. The revised film only tore 2% of the time, which was perfect for their fresh quinoa packaging. That’s why we don’t just rely on internal tests—we work with local partners in high-altitude regions to run on-site trials, because lab conditions can’t replicate every variable.
There are, of course, myths about thermoforming film at high altitudes that we encounter all the time. One common myth is that thicker film is always better. But in reality, too-thick film can cause more issues at altitude, because it requires more heat, and the uneven heat leads to inconsistent stretching. Another myth is that all films work the same as long as they’re labeled “high-altitude compatible.” A lot of suppliers market generic films as high-altitude without any testing, which is why so many customers have bad experiences. We don’t do that—every film we supply for high-altitude use is tested for elongation at low pressure, heat transfer at reduced atmospheric density, and barrier properties to prevent post-forming bulging.
The future of thermoforming in high-altitude regions is exciting, too. As e-commerce grows, more companies are shipping products between high and low elevations, so packaging has to handle pressure changes both during manufacturing and transit. We’re currently working on a stretchable thermoforming film that can accommodate pressure differences of up to 5 psi during transit, which would eliminate the puffing issue entirely. It’s still in trial phases, but early tests with a craft chocolate maker in Denver have shown that their bars stay in perfect packaging shape when shipped to customers in Miami, even though the pressure there is 50% higher than Denver’s.
At the end of the day, the short answer to “can thermoforming film be used in high-altitude areas” is a resounding yes—but not all thermoforming films. It’s not just about the film’s thickness or material; it’s about engineering a film that compensates for the unique pressure, temperature, and humidity conditions of high elevations. As a supplier, our job isn’t just to sell a product—it’s to partner with customers to figure out what combination of film, equipment adjustments, and testing works for their specific operation, whether they’re in a small bakery in Boulder or a pharmaceutical plant in La Paz.
If you’re a manufacturer working in a high-altitude region and have struggled with mold blowouts, package bulging, or high production waste, we can help. We have a team of application engineers who specialize in high-altitude thermoforming, and we offer free on-site trials to test our films in your facility. Reach out to our team to discuss your production challenges, and we’ll work with you to find a thermoforming film solution tailored to your needs.
Food Packaging Film References
- Thread, D., & Patel, R. (2021). The Impact of Atmospheric Pressure on Thermoforming Processes. Journal of Plastics Technology and Engineering, 60(3), 289-305.
- Garcia, M., et al. (2019). High-Altitude Packaging Challenges for Pharmaceutical Products. International Journal of Pharmaceutical Packaging, 12(2), 112-124.
- National Oceanic and Atmospheric Administration (NOAA). (2022). Atmospheric Pressure Variations by Elevation. U.S. Department of Commerce.
Wenzhou Fuya New Material Technology Co., Ltd.
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