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MIL SPEC AA-59588 Class 1 Silicones

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    Considering how strict military specifications (MIL SPEC) are for materials used in defense-related parts and devices, the number of silicones available under this class is nothing short of shocking. Dozens of materials fit the various MIL SPEC requirements, and they are divided into multiple sub-categories and classes within those sub-categories.

    It’s easy to get lost in the whirlwind of material types and specs when you’re designing a part, but this blog post is going to help with that. If you’re considering, looking for or working with MIL SPEC AA-59588 Class 1 silicones, you will find everything you need to know below.

    Modus Advanced is a premium manufacturing partner to defense engineers and contractors. In an industry that calls for utmost precision and absolute respect for the specs, there’s only one call to make: Modus Advanced.

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    About MIL SPEC AA-59588

    MIL SPEC AA-59588 is a specification from the U.S. General Service Administration (GSA). It divides defense- and aerospace-grade silicones into six grades and classes. These categories correspond to the hardness (durometer) of each material, as well as its temperature resistance.

    The classes of AA-59588 silicones are as follows:

    • Class 1A
    • Class 1B
    • Class 2A
    • Class 2B
    • Class 3A
    • Class 3B

    For the purposes of this article, we are discussing MIL SPEC AA-59588 Class 1A and 1B silicones.

    Class 1A and 1B AA-59588 Silicones

    Class 1A and 1B silicones under MIL SPEC AA-59588 share two primary unifying characteristics:

    1. They tend to be resistant to extremely low temperatures.
    2. They can reach high durometer levels of up to 80, although some can go as low as 40.

    Class 1B silicones offer an additional characteristic: at high temperatures, they have a low compression set. That means they won’t give much when placed in hot environments.

    MIL SPEC AA-59588 Class 1 Silicone Examples

    Below, we examine some examples of MIL SPEC AA-59588 Class 1 silicones from Specialty Silicone Products (SSP).


    SSP-122 meets the requirements of both Class 1A and Class 1B under MIL SPEC AA-59588. It is a silicone elastomer that is heat-cured and peroxide-catalyzed. It has a durometer of 60. Peroxide curing enables this material to resist corrosion or interference with materials like tin and latex, making it a common choice in automotive, industrial and aerospace applications.


    At a durometer rating of 50, SSP-227 is somewhat less hard than SSP-122, but it shares many of the same properties. It is cured with heat, catalyzed with peroxide and compliant with the strict requirements of AA-59588 Class 1A and 1B. That means this material is also ideal for many applications within aerospace, automotive and industrial environments.


    SSP-266 is the hardest of the AA-59588 Class 1 silicones from SSP. It has a durometer of 70. It is also peroxide-catalyzed and heat-cured, and it is used in many of the same applications as the other materials covered here. Also like the other Class 1 materials, SSP-266 offers resistance to low temperatures and a low compression set in higher temperatures.


    The softest of the SSP Class 1 AA-59588 materials, SSO-278 has a durometer of 40. Beyond that distinction, this material is highly similar to the other materials covered in the sections above. It is cured with heat and catalyzed with peroxide, and it is commonly used in defense, aerospace, industrial and automotive applications.

    Working with MIL SPEC AA-59588 Class 1 Silicones? Choose the Right Partner

    Any device that requires MIL SPEC AA-59588 silicones is bound to be pretty complex. By nature of having to comply with military specifications in the first place, you’re already working on a project that requires extreme precision. But when you get as granular as a sub-class of a MIL SPEC sub-category, you need the best manufacturing partner on the market.

    How do you go about finding that? Begin by examining any candidate’s quality certifications — particularly AS9100 if your device or part has specific aerospace or defense applications. After that, make sure the company works with this highly specific class of materials. (If you’re wondering, Modus Advanced works with all of the SSP materials listed above.)

    Finally, assess the manufacturer’s ability to provide design and engineering guidance throughout all phases of the process, including planning, prototyping and mass production.

    Modus Advanced: The Precise, Practical Manufacturing Partner

    The Modus Advanced team doesn’t just know MIL SPEC materials. We know the exact specifications of the tiniest sub-classes and categories within this group. And that includes MIL SPEC AA-59588 Class 1 silicones.

    That means we can act as not just a manufacturing partner, but a knowledgeable guide as you bring your part from concept to concrete. We can advise on material selection and design to help you make sure you get it exactly right, from paper to prototype to production.

    Ready to learn more about how we can help? Give Modus Advanced a call at 925-960-8700 or contact us online today.


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