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Does Temperature Affect Body Armor Performance?

Does temperature affect body armor? What NIST research says about heat and armor fibers, what CJTTEC advises about extreme heat and cold, how testing conditions armor, and how to store it.

ArmorList Editorial·January 13, 2025·6 min read

Understanding the performance of body armor includes knowing what heat, cold and sunlight can do to it. Whether you work in law enforcement, the military or security, armor spends hours in hot cars, cold nights and direct sun, and the sources have something to say about each.

Body armor is designed and tested to protect against ballistic threats, and the materials have been studied under heat, humidity and UV exposure. What the research shows is narrower than "temperature changes how armor performs", and it is worth reading exactly.

Understanding body armor basics

Body armor comes as soft armor, made of woven or laminated fibers, and hard armor plates of steel, ceramic or polyethylene, often with a fiber backing. CJTTEC, which administers the NIJ Compliance Testing Program, says NIJ 0101.07 names its levels "HG" for handgun and "RF" for rifle, with "a reduction in soft-armor levels and an additional hard-armor protection level". For the materials, read Materials Used in Armor Plates Explained.

Soft armor is commonly made from aramid (Kevlar is a para-aramid fiber that Stephanie Kwolek invented at DuPont in 1965; the brand now belongs to Arclin) or ultra-high-molecular-weight polyethylene (UHMWPE); the names identify fiber families, not the quality of a given product. For the levels hard armor is tested to, read Breaking Down Hard Body Armor Levels.

Each material has been studied differently, and the sources do not rank them by how sensitive they are to temperature. We found no NIJ or CJTTEC source that does (checked 1 October 2026).

How temperature impacts body armor materials

NIST research reports that heat during storage and use can reduce the strength of polyethylene fibers used in body armor, and with it their ballistic resistance. In a NIST study, a flexible UHMWPE unidirectional laminate lost less than 10% of its tensile strength after 336 days at 70°C.

For aramid, NIST exposed p-aramid yarns from two makers to combinations of temperature and humidity up to 70°C and 76% relative humidity for at least a year, and found them generally resistant to degradation, with changes of less than 10% only at the harshest conditions. For more on aramid, read How Effective Is Kevlar in Body Armor?.

The live version of this page said Kevlar and UHMWPE "can become brittle in extremely cold temperatures" and that rapid temperature changes cause "thermal stress". We found no NIJ, CJTTEC or NIST source for either (checked 1 October 2026). ASTM E3078, the practice NIJ 0101.07 Addendum 1 names for hard armor conditioning apparatus, includes thermal shock and temperature extremes procedures among others; users of the practice choose which apply.

Follow the manufacturer's temperature guidance for the exact model.

Effects of extreme cold on body armor performance

CJTTEC advises against storing armor where it may be exposed to extreme heat or cold, and NIJ's 2012 statement on body armor advises the same. We found no NIJ, CJTTEC or NIST source on how cold changes the ballistic performance of soft armor fibers, or on armor becoming brittle in the cold (checked 1 October 2026).

The live version of this page said "the performance of body armor can degrade by up to 20% in extreme cold" and cited NIST (2021). The NIST paper it named, on p-aramid fibers in the Textile Research Journal (2020), studied heat and humidity, not cold, and found p-aramid generally resistant. We found no NIST figure for cold (checked 1 October 2026), so the 20% is cut.

In our view, armor worn in the cold can feel stiffer and sit differently over winter layers; check fit with the clothing actually worn. Letting armor warm up before use is a comfort step, not a performance claim.

Effects of extreme heat on body armor performance

The heat finding the sources support is NIST's: heat in storage and use can reduce the strength of UHMWPE fibers, and in one NIST study a laminate aged for nearly a year at 70°C lost less than 10% of its tensile strength. We found no NIJ, CJTTEC or NIST source stating that heat makes soft armor "soften" in wear or lose structural integrity (checked 1 October 2026).

CJTTEC advises against storing armor where temperature, light and humidity are not reasonably controlled, such as a vehicle trunk, and advises storing it flat at room temperature in a dry, shaded place. Our advice: record heat exposure in the armor's history alongside its inspections, because a heat effect on fibers is not something the sources say you can see.

The role of UV radiation in armor degradation

NIJ names ultraviolet and visible light among the factors that may contribute to the degradation of fibers used in body armor. CJTTEC advises protecting armor from UV light and storing it in a shaded place that limits exposure to direct light.

In our view, the practical step is simple: keep armor, and especially the ballistic panels, out of direct sun when it is not being worn, and keep the carrier on.

Importance of proper storage and maintenance

CJTTEC's guidance, and the maker's label, come first. CJTTEC advises storing armor flat at room temperature in a dry, shaded place, out of vehicle trunks, and air-drying panels flat without folding or creasing them. It advises against dry cleaning, machine washing or submerging panels; its steps are to wipe the panel cover with a damp sponge or soft cloth and cold water. CJTTEC notes that NIJ requires manufacturer care instructions on the label of every compliant model. For more, read How to Maintain and Care for Body Armor.

NIJ said in 2012 that age alone does not cause body armor's ballistic resistance to deteriorate, and that the care and maintenance of vests are vital. CJTTEC warns against assuming that a hard plate's good appearance means good performance, so inspection catches only the visible part.

Tips for maintaining armor in various climates

Our advice, built on CJTTEC's storage guidance:

  1. Do not leave armor in a vehicle trunk or cabin in heat or cold; store it at room temperature, flat, dry and shaded (CJTTEC).
  2. Keep it out of direct sun when not worn (CJTTEC: protect from UV).
  3. In cold weather, check fit over the layers actually worn.
  4. Inspect after unusual exposure, log it, and ask the maker if anything looks wrong.

Conclusion and key takeaways

The sources say less about temperature than the live page did, and what they say is specific. NIST found heat can reduce UHMWPE fiber strength, and found p-aramid generally resistant to heat and humidity. NIJ names heat, moisture and light among factors that may degrade fibers. CJTTEC advises keeping armor away from extreme heat or cold and out of direct light.

Store armor as CJTTEC and the label say, record what it has been exposed to, and check the model's listing with the date you read it. On ArmorList, a product's record shows its NIJ CPL status with the date the list was read, and the standards it was tested to.

Sources

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