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MIL SPEC AA-59588 Class 2 Silicones

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    When you’re designing a highly sensitive part or device — such as the kinds common in the defense and aerospace industries — you have virtually endless materials to choose from, but only a handful will actually deliver the right technical performance, meet all standards of quality and other specifications and keep you within the project’s budget. 

    Often, materials that fit that description for defense applications are MIL SPEC AA-59588 Class 2 silicones. But even within this category, you still have some decisions to make. That’s what this blog post aims to help you with. Keep reading to learn everything you need to know about this unique class of military-grade silicone materials. 

    You can’t compromise on quality in manufacturing — especially when you’re working with MIL SPEC parts and devices. The team at Modus Advanced knows how important quality is, and it’s why we hold ourselves to the highest standards and work with the best materials. Want to work with us? Reach out today.

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    Understanding MIL SPEC AA-59588 Class 2 Silicones

    To fully understand this class of silicones, we need to first understand what MIL SPEC is. This is simply a designation that shows that a material is up to standards set for defense and aerospace applications. MIL SPEC AA-59588 is one of those sets of standards.

    More specifically, MIL SPEC AA-59588 divides silicones into six categories based on their hardness and temperature resistance: Class 1A, Class 1B, Class 2A, Class 2B, Class 3A and Class 3B.

    Classes 2A and 2B make up Class 2, and those are the silicones we are discussing in the rest of this post. What sets Class 2 MIL SPEC AA-59588 apart from Classes 1 and 3 is the relatively simple matter of temperature resistance. While Class 1 and 3 silicones are resistant to cold temperatures, Class 2 silicones are resistant to high heat. 

    In many other respects, such as the range of durometers you can find within this class of silicones, MIL SPEC AA-59588 Class 2 silicones are similar to the other two classes. But as any engineer or designer who has worked in aerospace or defense can tell you, temperature resistance is a pretty big deal.

    Examples of Class 2 Silicones Under MIL SPEC AA-59588

    When you’re trying to gain a broad understanding of a class of materials, it’s often helpful to look at some real examples. We have provided those examples below. Each of the following MIL SPEC AA-59588 Class 2 silicones comes from Specialty Silicone Products (SSP), a materials manufacturer known for its unparalleled level of quality.


    At a durometer of 40, SSP-220 is one of the softer MIL SPEC AA-59588 Class 2 silicones. Durometers in this class can reach 80, and 40 is on the lower end of what you will find. This is a heat-cured silicone catalyzed with peroxide. It meets the strict requirements of both Class 2A and Class 2B.


    Heat-cured and peroxide-catalyzed in the same way as SSP-220, SSP-301 is slightly harder at a durometer of 50. This silicone elastomer is up to the specs of Class 2A and Class 2B.


    SSP-352 hovers around the middle of the pack in terms of hardness. With a durometer of 60, this 2A- and 2B-compliant silicone elastomer occupies the Goldilocks zone of not too hard and not too soft. Like the other materials in this class, it is heat-cured and peroxide-catalyzed.


    Nearing the harder upper limit of the spectrum of MIL SPEC AA-59588 Class 2 silicones is SSP-389 with a durometer of 70. It’s also cured with heat and catalyzed with peroxide.


    With a durometer of 25, SSP-390 is, by a large margin, the softest of the silicones in Class 2. It still meets all the requirements of AA-59588 Class 2A and 2B, and it’s peroxide-catalyzed and heat-cured.


    SSP-391 is the hardest of this class of silicones. It has a durometer of 80, meets all AA-59588 requirements for Class 2 and is heat-cured and peroxide-catalyzed.

    Choosing the Right Partner when Working with AA-59588 Class 2 Silicones

    As you can see, there are plenty of AA-59588 Class 2 silicones to choose from, and there’s a nearly equal number of manufacturing partners who would love your business as you develop a part made from these materials. But you need the best — not just the first one you find.

    How do you find the best manufacturing partner, one that can work with highly sensitive devices, materials and specifications? You have to start with quality. Ask the manufacturing partner about their quality assurance processes, as well as their specific experience with MIL SPEC AA-59588 Class 2 silicones. 

    If they can’t give a satisfactory answer for both questions, move on to the next candidate.

    Modus Advanced: Here to Help at Every Step

    Whether you’re actively looking for a manufacturing partner or simply in the planning stage, the manufacturing partner you choose matters just as much as the materials you choose. You need a manufacturing partner who can not only work with MIL SPEC AA-59588 Class 2 silicones, but advise you at every stage of the process. 

    The Modus Advanced team is prepared to do exactly that. With top-tier engineers, quality professionals and manufacturing experts making up the backbone of our industry-leading team, we have what it takes and much more.

    Ready to work with the last manufacturing partner you will ever need? Drop Modus Advanced a line. Give us a call at 925-960-8700 or contact us online.


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