Evaluating Plastic Tank Manufacturers

Blow Molding

Choosing a manufacturer for your custom plastic tanks can be a daunting task. In fact, a simple Google search for plastic tank manufacturers returns 32 million results. And there are over 650 plastic tank suppliers on Thomasnet!

A screenshot of plastic tank manufacturer listings on Thomasnet and Google.

Luckily, some online manufacturer directories such as Thomasnet allow you to narrow your search by product/process, location, company type, and other basic criteria. Just beware of the directories that have a relatively low number of listings – this is a sure sign that the directory only works with suppliers that pay for a listing, meaning their database is small and the results likely are biased.


Now that you’ve searched and narrowed your options, it’s time to decide who you’re going to work with. It can be tempting to paste your shortlist to a wall and toss a dart to decide, but with a little more leg work you’ll separate the manufacturers that can give your company a competitive edge from the ones who are full of hot air.

Evaluation Criteria

There are suppliers that are merely capable, and then there are suppliers that have the design, engineering, and manufacturing expertise you need to optimize your design and drive cost out. To find the latter, evaluate your shortlist suppliers on their certifications, product and industry experience, molding methods, material expertise, tooling options, prototyping process, testing abilities, in-line and secondary processes, and ability to hold your tolerances. Let’s take a look at each one.



Certifications in manufacturing are a dime a dozen, so don’t be wooed by a wall or a webpage covered with them. If you really want to spot the master in a crowd of novices, look for these quality and environmental certifications:


Quite simply, if you want a high quality tank, you need a high quality supplier. A certification from the International Organization for Standardization (ISO), the leading authority on quality and environmental standards, is a convincing vote of confidence.

ISO 9001 – Intended for use by any organization, the ISO 9001 certifies that systems are in place and are continually improving to deliver quality products. It requires that step-by-step, detailed processes and procedures are in place to ensure quality in the manufacturing, storing, testing, and shipping of products.


When you work with an ISO 9001 certified company, you can rest easy knowing they have a constant and systematic commitment to meeting your tank specifications every time, all of the time.


ISO/TS 16949* – Intended for use by suppliers to the automotive industry, the ISO/TS 16949 includes all requirements of the ISO 9001, with additional technical specifications (TS) put forth by the International Automotive Task Force (IATF), a group of automotive OEMs including Ford, GM, and FCA. It includes new sections in regards to responsibility, competence, training, and awareness, and heavily amends the control of product and service section to include requirements on control plans, work instructions, preventive and predictive maintenance and tool management.


When you work with an ISO/TS 16949 certified company, you’re working with an industry-leading company that will go the extra mile to deliver the best tank possible with zero defects.

*The ISO/TS certification is in the process of migrating to IATF 16949:2016. Updates will be made to this post as soon as the migration is complete.


ISO 14001 – The ISO 14001 certifies an effective system is in place that enables the company to manage and enhance its environmental performance. Rather than setting performance requirements, the ISO 14001 provides a framework with which a company can use to continually minimize its negative impact on the environment while staying in compliance with applicable laws and regulations.


When you work with an ISO 14001 certified company, you have confidence that resources are being used efficiently and waste is being minimized, in turn reducing the cost of producing your plastic tank.

For a supplier with all of these certifications, look no further than Regency Plastics, a Gemini Group company.


You wouldn’t go to a foot doctor for heart surgery. The same rationale applies to the production of your plastic tank. Every manufacturer has a unique set of strengths and weaknesses. One with experience in your industry can offer innovative ideas to enhance your tank. One with experience in plastic tanks will have built-in efficiencies that save you time and money. Any way you cut it, it’s usually best to choose a supplier with a proven track record for your industry and/or product.


Molding methods

There are two main molding methods for producing hollow containers; extrusion blow molding and rotational molding. The best choice for your tank depends on your part size, geometry, and quantity.


Blow molding is typically better for tanks smaller than five square feet, whereas rotational molding is better suited for larger tanks.


Although double wall construction is possible with blow molding, rotational molding may be more cost-efficient. For local complexities, however, blow molding is usually superior.


Blow molding is best for large volume production of at least 3,000 parts annually, while rotational molding is more efficient at lower volumes.

Material expertise

Material selection is one of the most important decisions you’ll make for your tank. It affects cost, weight, manufacturability, and performance. As such, you’d be well-served to find a supplier that has extensive experience in working with common tank materials such as HDPE, polypropylene, PVC, PE, and polyethylene.


Even if you’ve already chosen a material for your tank, a supplier with expertise in material selection can identify additives that will enhance the resin’s properties while reducing manufacturing costs.



Your choice of plastic tank manufacturer will have a drastic impact on the quality and build-time of your tooling.

Two men building tooling for custom plastic tank manufacturing.

Rotational molding tooling is typically built with a softer metal like aluminum and will need to be refurbished or replaced every 3,000 cycles, whereas blow mold tooling can last for hundreds of thousands, if not millions, of cycles.


Regardless of which manufacturing process you choose, always ask your supplier where the tooling is coming from – if they source their tooling from China, for example, the quality will be significantly lower than the same tooling sourced from the Unites States and can result in serious issues with conformity and repeatability.


The best option is to choose a supplier with in-house tooling capabilities. They can offer you shorter turnaround times and can respond quickly to tooling changes.



If you’re design hasn’t yet been built and tested, you’ll need to first build a prototype as a proof of concept. Not all suppliers have experience with this stage of development, so ask your candidates for examples of their work in prototyping. Some suppliers will have software that simulates the molding method, such as Regency Plastic’s B-Sym blow molding simulation software


If you want to ensure that your plastic tank meets all dimensional and functional requirements, choose a supplier with a variety of testing methods. Testing should be performed before (PPAP – pre production approval process), during (in-process testing), and after the molding process. For plastic tanks, in particular, look for a supplier that has leak-testing capabilities and a strong quality management system in place.


Secondary processes

Your plastic tank will most likely require some type of secondary processing. Look for a supplier that specializes in processes such as plastic welding, riveting, and staking.


To minimize rejection rates and waste, choose a supplier that offers partial or full automation of these processes. Another secondary process to consider is assembly. If your tank requires a cap or pump, choose a supplier that has dedicated staff and equipment to handle your tank assembly.



Not all plastic tank manufacturers can hold the same tolerances. It all depends on the molder’s processes, technologies, and experience. In terms of processes, blow molding has a wider range of tolerances than rotational molding due to the variety of blow molding methods and technologies. For example, the extrusion blow molding method can hold tighter tolerances than rotomolding, but the injection and stretch blow molding methods fall short of rotomolding.


The experience of the molder will also influence the degree of tolerances they can achieve. The most experienced blow molders employ a method called technical blow molding, wherein strategies are employed within both the blow molding process and secondary processes to achieve the tightest tolerances. For this reason, most plastic tanks found in the automotive industry are produced with this method.


If your tank has complex local features that require tight tolerances, your best bet is to choose a technical blow molder.

Get Started

If you’re looking for a high quality supplier for your plastic tank, start by reviewing your candidates’ certifications.

A certification from the ISO demonstrates that they’ve invested heavily in meeting the most demanding quality and environmental standards, so they’re probably worth a call. Use the template below to further evaluate your options.

Supplier Evaluation Checklist

1. Certifications

□ ISO 9001
□ ISO/TS 16949
□ ISO 14001

2. Experience








3. Molding Methods

□ Extrusion Blow Molding
□ Injection Blow Molding
□ Stretch Blow Molding
□ Rotational Molding



4. Material Expertise

□ HDPE, polypropylene, PVC, PE, polyethylene
□ Additives



5. Tooling

□ In-house
□ 3rd party

6. Prototyping

□ Simulation software

□ Dedicated sales staff and equipment



7. Secondary Processes

□ Welding
□ Riveting, Staking, Etc.
□ Assembly



8. Tolerances

Typical Tolerances




Strategies To Improve Tolerances



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