What’s the moisture resistance of blown stretch film, and why does it matter for your shipments? Let’s be real—if you’re shipping goods, especially ones that can get ruined by dampness, that stretch wrap you’re using isn’t just a “wrap-it-and-go” kind of thing. I’ve been in the blown stretch film game for over 12 years now, and I can’t tell you how many times a customer has called me panicking because their pallet of electronics parts, food-grade packaging, or raw materials showed up with water damage—and half the time, it’s because they didn’t pay attention to their film’s moisture resistance. So let’s break this down like I’d break it down for a new guy on the production line, no fancy jargon, just straight facts. Blown Stretch Film
First off, what even is blown stretch film, vs. cast stretch film? I know a lot of people mix them up, but here’s the quick version: blown film is made by extruding plastic resin through a round die, blowing air to bubble it up, then cooling it before stretching. That process gives it a different molecular structure than cast film (which is flat, cooled fast). That structure directly impacts moisture resistance—so that’s why the two types aren’t interchangeable for jobs where damp is a risk.
Now, moisture resistance isn’t a “one-size-fits-all” number. You can’t just say “this film is moisture resistant” and be done with it. It’s measured by something called water vapor transmission rate (WVTR), right? Yeah, WVTR is the amount of water vapor that passes through a material in a set amount of time, usually grams per square meter per 24 hours (g/m²/day). The lower the number, the less vapor gets through—so the better the moisture resistance. But here’s the thing: blown stretch film’s WVTR isn’t static. It changes based on the resin we use, the thickness of the film, and even the environmental conditions when you’re using it.
Let’s talk resin first. Most blown stretch film is made with linear low-density polyethylene (LLDPE), but we mix in other resins sometimes—like low-density polyethylene (LDPE) or even metallocene LLDPE (mLLDPE) to improve stretch. Wait, why does resin matter for moisture? Polyethylene itself is a pretty good barrier to moisture, but not perfect. If you use a pure LLDPE blend, our standard 80-gauge blown film has a WVTR around 5-7 g/m²/day. But if we add a bit more LDPE (which is a bit more flexible, but still has similar barrier properties), we can tweak that to 4-6 g/m²/day. Now, if you need way better moisture resistance—like for shipping agricultural goods that need to stay dry in a rainy warehouse, or bulk chemicals that can’t absorb moisture—we can go with a co-extruded blown film. That’s when we layer different resins: the core layer is for strength, and the outer layers are made with a slightly modified PE that’s a tighter barrier. Those co-ex films have a WVTR closer to 2-4 g/m²/day. That’s a big difference, right?
Then there’s thickness. This is a huge one I see customers sleep on. Thicker film = better moisture resistance, mostly. A 60-gauge blown film (that’s 15 microns, for anyone who uses microns) will have a higher WVTR than a 100-gauge (25 microns) film of the same resin blend. Wait, let’s make that relatable: if you’re wrapping a pallet of furniture for storage, a thin 60-gauge might be fine for a week or two, but if you’re storing it outside for a month, that thin film might let enough moisture in to cause mold on the wood. Crank that up to 100-gauge, and the WVTR drops, so your pallet stays dry longer. I always tell customers to match thickness to their timeline and storage/transport conditions—no need to pay for 100-gauge if you’re just moving pallets across a dry factory floor.
But here’s a catch: moisture resistance isn’t the only thing. Blown stretch film also needs to stretch, right? That’s the whole point—you wrap it tight, it clings to itself, holds the pallet together. If we make the film too thick, or tweak the resin too much for a better moisture barrier, it might lose its stretchability. No one wants a film that won’t stretch 200% like it’s supposed to, because then you can’t get a tight wrap. We balance that every day in our lab—test different resin blends and thicknesses so you don’t have to choose between holding your pallet tight and keeping moisture out.
Now, let’s talk about when moisture resistance actually matters, because not every shipment needs top-tier WVTR. If you’re shipping dry goods like metal parts that rust if damp, or frozen food that can develop freezer burn (wait, freezer burn is actually from moisture loss, right? Oh, right—if the film isn’t a good moisture barrier, the ice in the food sublimates out, so you get freezer burn), or raw materials like powdered chemicals that clump up when they get even a little damp—then moisture resistance is non-negotiable. I had a customer a few months back who was shipping powdered detergent to a overseas market. They were using cheap thin blown film, and by the time the shipment got to the port, half the pallets had clumped powder because the film let in humid ocean air. They switched to our 90-gauge co-ex blown film, and haven’t had a problem since. That’s the kind of thing I’m talking about—getting the right moisture resistance saves you from losses, not to mention the hassle of returns.
Wait, but what about outdoor use? If you’re wrapping pallets outside, in rain or high humidity, the film’s moisture resistance has to hold up even in extreme temps. Cold weather, for example—PE gets stiffer when it’s cold, right? Does that affect moisture resistance? Surprisingly, no—because the molecular structure of PE stays pretty consistent in cold temps, unlike some other plastics. High humidity when you’re wrapping, though—if you wrap a pallet in 90% humidity, the film might cling a little differently, but the moisture barrier itself doesn’t change much. I’ve tested our film at 30°F and 90°F, and WVTR only shifts by like 10-15%, which is negligible for most applications. The big thing with outdoor wraps is also UV resistance, but that’s a separate conversation—though we can blend UV inhibitors into our blown film too, so you get both UV protection and good moisture resistance.
Is there a myth I hear all the time? That “all blown stretch film is the same for moisture resistance.” No way. I’ve seen cheap blown film from overseas suppliers that has a WVTR of 10 g/m²/day or higher—because they use lower-grade resin, skip the proper cooling during extrusion, so the molecular gaps are bigger, letting moisture seep through way easier. That’s why it’s not just about the label, it’s about working with a supplier that tests their film’s WVTR regularly. We test every batch we make in our in-house lab—no exceptions—so we can give you exact numbers, not guesses.
Another thing: cling. Wait, cling is different from moisture resistance, but they can play off each other. If your film has good cling, it’s tighter on the pallet, which actually reduces the amount of surface area where moisture could seep in around the edges. But that’s a secondary benefit—you still need the WVTR to be low enough. We add cling agents to our blown film, so you get the tight wrap and the moisture barrier at the same time.
So how do you pick the right moisture resistance for your needs? Let’s break it down quick:
- If you’re shipping short distances (under 50 miles), dry warehouses, no sensitive goods: 60-80 gauge standard LLDPE blown film, WVTR 5-7 g/m²/day is enough.
- If you’re shipping longer distances, moderate humidity, semi-sensitive goods (metal parts, non-clumpy powders): 80-90 gauge blended blown film, WVTR 4-6 g/m²/day.
- If you’re shipping overseas, outdoor storage, high humidity, super sensitive goods (food, chemicals, electronics): 90-120 gauge co-ex blown film, WVTR 2-4 g/m²/day.
That’s a rough guide, but every shipment is different. Maybe you have a pallet that’s going to sit on a dock for 2 weeks before shipping, so you need a bit more barrier. Maybe your goods can handle a little damp, so you can go thinner. The worst thing is using too much, because you’re paying for thicker film than you need—we hate that too, because we want our customers to get the best value, not just more product.
Wait, let’s address a common question: can moisture resistance change over time? Like, if the film is on a pallet for 6 months, does it start letting more moisture in? For standard blown PE, no—PE is pretty stable. The WVTR stays consistent for like 1-2 years, as long as you store the film in a cool, dry place (which we always recommend—don’t leave rolls in the sun, that can break down the resin and hurt barrier properties). If the film is stored right, moisture resistance doesn’t degrade much over time. That’s important for long-term storage, like if you’re wrapping pallets for a warehouse hold.
I know, this sounds like a lot, but it’s all about matching your film to your use case. If you’re not sure, just reach out. We don’t do one-size-fits-all here—we’ll ask you what you’re shipping, where it’s going, how long it’s wrapping, and then we’ll recommend the exact blown stretch film with the right moisture resistance. No pushy sales talk, just straight answers. We’ve been in this business long enough to know that the best partnerships are when we help you solve a problem, not just sell a product.
At the end of the day, blown stretch film’s moisture resistance is a make-or-break feature for a lot of shipments. Skip testing, skip matching the right resin and thickness, and you’re looking at ruined goods, lost money, upset customers. We don’t want that for you. So if you’re tired of dealing with film that doesn’t protect your goods from moisture, or you’re just trying to figure out which film is right for your next shipment, hit us up to connect and chat through your needs. No hidden fees, no confusing specs, just a clear recommendation that works for your budget and your products.
Packaging Labels References:
- Harper, C. A., & Petrie, E. M. (2010). Plastic Materials and Processes. McGraw-Hill.
- Sorrentino, A., Gorrasi, G., & Vittoria, V. (2007). Potential of biopolymers in packaging applications. Trends in Food Science & Technology, 18(4), 184-196.
- American Society for Testing and Materials (ASTM). (2018). Standard Test Method for Water Vapor Transmission Rate of Flexible Barrier Materials (ASTM E96). ASTM International.
- Welle, F. (2011). Translate-rules for the mechanical recycling of polyolefin packaging waste. Waste Management, 31(9), 1916-1927.
Huizhou Yufeng New Materials Co., Ltd.
Address: 9th Floor, Building A9, Zhongchuang Yingke New Generation Industrial Park, Tonghu Town, Huicheng District, Huizhou City
E-mail: liangjun@kaiyudianzi.com
WebSite: https://www.yufengstickers.com/
