If you’ve ever stopped to think about how the shampoo bottle in your shower, the gallon jug of water you grab from the grocery store, or the toy your kid brought home from the last birthday party got made, chances are it passed through a blowing molding machine. For decades, I’ve been in the business of supplying these machines—working directly with factory owners, production managers, and material engineers who tell me the biggest question they ask isn’t “Does this machine work?” It’s “What can I actually run in it?” The answer isn’t as simple as a single material, either. Over the years, I’ve seen factories swap out resins to cut costs, improve product safety, or adjust how their final parts hold up in extreme temperatures, and I’ve learned to guide them through every choice. Let’s break this down, from the most common materials to the niche ones that make specific products possible, plus what every new buyer should know before they lock in a machine order. Blowing Molding Machine
First, there’s the workhorse of the blowing molding world: High-Density Polyethylene, or HDPE. If you’ve ever picked up a 5-gallon water jug, a laundry detergent bottle, or a plastic trash can, you’ve held HDPE. It’s the most popular material for extrusion blowing molding (the style most people mean when they talk about blowing molding, where melted resin is forced through a die into a tube called a parison, which is then blown into a mold) because it’s tough, flexible, and cheap. I’ve had small detergent factories tell me they switched to HDPE from PET because it doesn’t crack when it’s filled with harsh cleaners, and it weighs less—cutting shipping costs by 15% almost overnight. The catch with HDPE, though, is that it’s not great for clear parts; it has a milky, opaque finish because of how its molecules bond. If a customer wants a clear beverage bottle, HDPE usually isn’t the first call.
That’s where Polyethylene Terephthalate, or PET, comes in. PET is the material behind soda bottles, water bottles, and even some food jars. It’s lighter than glass, super clear, and has excellent barrier properties—meaning it keeps carbonation in soda and oxygen out of canned goods, which is why it’s the go-to for soft drink manufacturers. I work with a beverage packaging plant that runs 100-ton blowing molding machines 24/7 on PET, and they told me that with the right machine settings, they can produce 1,200 small water bottles every hour. The only downside to PET is that it’s stiffer than HDPE, so it can’t handle extreme cold as well—leave a PET water bottle in your car on a winter day, and it might crack when you try to unscrew the cap. It also doesn’t hold up to harsh chemicals the way HDPE does, so it’s not used for things like drain cleaner bottles.
Next up is Polypropylene, or PP. This is the jack-of-all-trades for tougher applications. I’ve seen PP used for everything from baby formula bottles to car parts like battery casings and interior trim. It’s more heat-resistant than both HDPE and PET—you can boil a PP bottle to sterilize it, which is why it’s perfect for baby products. It’s also more rigid than HDPE, so it works for items that need to keep their shape, like medication bottles or food containers that stack on grocery store shelves. One of my newer customers, a manufacturer of outdoor garden tools, switched to PP last year to make small trowel handles; the PP parts don’t bend when someone’s digging in hard soil, and they can survive being left in the sun for years without fading. The only thing to watch with PP is that it can leave a slightly sticky residue if you’re running it at the wrong temperature, so the machine’s heating and cooling settings matter here a lot more than with some other materials.
Then there’s Low-Density Polyethylene, or LDPE. LDPE is softer and more flexible than HDPE, which is why it’s used for things like plastic grocery bags, squeeze bottles for ketchup or mustard, and cling wrap. Wait, you might be thinking—aren’t grocery bags made with a different process? A lot of people confuse blowing molding with the thin film used for bags, but actually, thin film blowing is a specific type of extrusion blowing molding, and LDPE is still the main material for that. I’ve had a customer who makes compostable LDPE bags (wait, no—wait, I’ll get into biodegradable options later) make traditional LDPE bags, and they told me LDPE is easy to run on most standard blowing molding machines, even older models. The downside is that LDPE is less durable than HDPE, so it tears more easily; that’s why grocery stores switched to thicker HDPE bags a few years ago. But for flexible, lightweight items, LDPE is irreplaceable.
Now, moving into the more specialized materials that I only recommend for specific projects. There’s Acrylonitrile Butadiene Styrene, or ABS. ABS is a hard, impact-resistant plastic that’s used for things like toy parts, refrigerator door liners, and even small industrial containers. I worked with a toy company last year that switched to ABS for their action figure packaging; the ABS can hold up to being dropped on a warehouse floor without cracking, which meant they cut their damage rate by almost 20%. The thing with ABS is that it melts at a higher temperature than most common plastics, so you need a machine with a more powerful heater and better temperature control to run it right. If a buyer tries to run ABS on a machine that’s set up for HDPE, they’ll end up with lopsided parts that don’t hold their shape.
Then there’s Polyvinyl Chloride, or PVC. PVC is a controversial material these days, but it’s still used for some blowing molding applications, like clear medical tubing, window frames, and even some bottled water (wait, no, most bottled water is PET—PVC was used for old juice bottles, but that’s mostly phased out). The issue with PVC is that it releases small amounts of chlorine during the melting process, which can be bad for the machine’s internal parts if you don’t have proper ventilation. That’s why I only suggest PVC for customers who have industrial-grade ventilation systems and are willing to do regular maintenance on their machines. It’s also not food-safe, so you can’t use it for any product that touches food or drink. I had one customer who made PVC pipe fittings for construction, and he told me that with the right exhaust system, his machines have run on PVC for 10 years without major issues—but he wouldn’t recommend it for anyone making consumer goods.
Now, the big trend I’ve seen in the last five years: biodegradable and recycled materials. Customers keep asking for ways to make their parts more eco-friendly, so I’ve been working with resin suppliers to test PLA (Polylactic Acid), which is made from corn starch, and recycled HDPE (rHDPE). PLA is great for single-use items like food containers and utensils, but it has a big downside: it only breaks down in industrial composting facilities, not in home compost, so I have to warn customers about that. rHDPE is a big hit with grocery store chains that want to use recycled plastic for their shopping bags; I’ve had a national grocery chain install four of my machines specifically to run rHDPE, and they told me it cuts their plastic waste by 80% compared to using virgin resin. The key with recycled materials is that they’re often less consistent than virgin resin—one batch might have a different melt point than the next, so the machine needs to have adjustable controls to handle that. I always tell new buyers that if they’re going to run recycled materials, they should budget a little extra for machine upgrades that let them tweak settings on the fly.
Now, let’s talk about what every buyer gets wrong when they’re picking a material. A lot of first-time factory owners come to me saying, “I want to run the cheapest resin possible.” But that’s not always the right call. For example, if you’re making a bottle for motor oil, HDPE is cheaper, but PP is better because it doesn’t crack when it’s exposed to oil residues. Or I had a customer who tried to run a cheap, low-grade LDPE to make squeeze bottles; the bottles would leak because the resin was too thin, and they had to replace half their machine’s dies within a month. The other mistake is not checking if the machine can actually handle the material. For example, a 5-ton small desktop blowing molding machine (used for small parts like toy caps) can’t run ABS, because ABS needs more heat and pressure to melt properly. I always spend at least 30 minutes with a new customer going over their product specs, their production volume, and their budget, because matching the material to the machine is just as important as matching the machine to the product.
I’ve been doing this for 22 years, and I’ve seen factories lose thousands of dollars because they picked the wrong material for their machine. One time, a small manufacturer of outdoor furniture ordered a machine to run HDPE, and then tried to switch to PP without telling me. The machine’s heater wasn’t powerful enough for PP, so their parts came out lopsided, and they had to pay to upgrade the heater—costing them $8,000 in unexpected expenses. Now, I make it a point to ask every new customer to bring a sample of the part they want to make, or at least a detailed description, so I can tell them exactly what materials work, and what machine upgrades they need.
At the end of the day, the blowing molding machine isn’t a one-size-fits-all tool. It can run a dozen different materials, each with their own pros and cons, and each requiring specific settings to get a good product. The best part of my job is helping customers figure that out—whether they’re a small startup making dog toys, or a large corporation making food packaging. I don’t just sell machines; I help people find the right tools for their products, so they don’t waste time or money on something that doesn’t work.
If you’re in the market for a blowing molding machine, or you’re thinking of switching materials to improve your products or cut costs, I can help you walk through every option. We can talk about your production volume, the type of parts you make, and your budget, and I’ll give you honest advice on what materials will work best for your machine. There’s no one-size-fits-all answer, but there’s always a solution that fits what you’re trying to make.
Plastic Bucket Crate Injection Molding Machine References
Rosato, D. V., & Rosato, M. G. (2004). Blow Molding Handbook. Hanser Publishers.
Speedy, C. S. (2019). Sustainable Polymers for Blow Molding Applications. Journal of Applied Polymer Science.
ASTM International. (2021). Standard Guide for Blow Molding Material Selection. ASTM D6100-21.
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