Breakthrough time is the amount of time it takes for a chemical to pass completely through a protective material, such as a glove or suit, and reach your skin. It’s measured in minutes under standardized lab conditions, and it’s the single most important number for choosing the right protective equipment when you work with hazardous chemicals. A glove with a breakthrough time of 4 hours against a specific solvent, for example, means you have roughly 4 hours of protection before that chemical starts coming through the other side.
The key thing to understand: all chemicals will eventually permeate protective clothing. Breakthrough time tells you how long you have before that happens.
How Chemicals Move Through Protective Materials
Breakthrough time measures a process called permeation, which is different from a chemical leaking through a hole or tear. During permeation, individual molecules of the chemical enter the outer surface of the material and essentially “squirm” through the spaces between the material’s own molecules until they emerge on the inner side. The glove or suit can look completely intact to the naked eye while this is happening. There’s no visible damage, no obvious sign that the chemical is getting through.
This is what makes breakthrough time data so critical. You can’t tell by looking at or touching a glove whether a chemical has started permeating it. The only way to know is to check the manufacturer’s test data for that specific chemical and material combination before you start working.
How Breakthrough Time Is Measured
The standard test method comes from ASTM (the American Society for Testing and Materials), specifically test method F739. A small piece of the protective material is placed in a test cell, and the chemical is applied to one side under continuous contact. On the other side, a collection stream picks up any molecules that make it through. Sensitive analytical instruments monitor that collection stream, and the clock starts ticking from the moment the chemical first touches the material.
Breakthrough is officially recorded when the permeation rate reaches a threshold of 0.1 micrograms per square centimeter per minute under the ASTM standard. The European standard (EN 16523-1) uses a slightly higher threshold of 1.0 microgram per square centimeter per minute. This difference matters: the same glove tested against the same chemical can show a longer breakthrough time under the European method simply because it uses a less sensitive detection level.
European standards also use breakthrough time to classify protective gloves into performance categories. Category A gloves must resist at least six chemicals from a standard list for 30 minutes or longer. Category B requires the same 30-minute threshold for at least three chemicals. Category C requires just one chemical to hold for at least 10 minutes.
Breakthrough Time vs. Permeation Rate
These two numbers often appear together on manufacturer data sheets, and they measure different things. Breakthrough time tells you when the chemical first gets through. Permeation rate tells you how fast it flows through once it does. Think of it like a dam: breakthrough time is when the first water spills over, and permeation rate is how much water pours over per minute once the flow is established.
Both numbers matter for safety decisions. A material might have a long breakthrough time but a very high permeation rate once that time is reached, meaning exposure ramps up quickly. Another material might allow slow, steady permeation that builds gradually. Checking both values gives you a more complete picture of how long your protection will actually last in practice.
Why Real-World Protection Is Shorter
Lab tests run under controlled conditions: room temperature, a flat piece of material, no stretching or flexing. Real work environments are different, and several factors can significantly shorten how long a glove or suit actually protects you.
Temperature is the biggest variable. When researchers tested natural rubber latex gloves against pesticides at body temperature (37°C) instead of room temperature (25°C), breakthrough times dropped by 27%. Some materials fared worse. One nitrile glove that lasted 53 minutes at room temperature broke through in just 27 minutes at body temperature, a 49% reduction. Depending on the chemical and material, warming from room temperature to skin or body temperature can cut breakthrough time by 20 to 50%.
Material thickness also plays a direct role. Thinner gloves permeate faster. Stretching a glove over your hand thins the material, especially across the knuckles and fingertips, which are often the areas with the most chemical contact. Physical wear, abrasion, and repeated flexing during tasks can further reduce effective thickness.
Permeation vs. Degradation
These are two separate ways a chemical can compromise your protective equipment. Permeation is the invisible molecular process described above. Degradation is visible physical damage: the material becomes hard, brittle, soft, swollen, or weak after chemical contact. You can usually see or feel degradation happening.
They don’t always go hand in hand. A glove might show no signs of degradation while a chemical quietly permeates through it. Conversely, a chemical that quickly degrades a material will almost certainly destroy its permeation resistance too. Manufacturers typically won’t even test permeation for chemical and glove combinations that score poorly on degradation, because the material falls apart before a meaningful breakthrough time can be recorded.
How to Use Breakthrough Time Data
Glove and suit manufacturers publish chemical resistance guides that list breakthrough times for specific chemicals against specific materials. These charts are the starting point for selecting protective equipment. When you look up a chemical, you’ll find breakthrough times ranging from under 10 minutes (essentially no useful protection) to over 8 hours for well-matched materials.
A few practical guidelines for interpreting the data:
- Match the exact chemical. Breakthrough times are specific to individual chemicals. A glove that resists one solvent for hours might fail against a similar solvent in minutes. Mixtures of chemicals can behave differently than either chemical alone.
- Build in a safety margin. Because lab conditions are more controlled than real work, most safety professionals recommend replacing gloves well before the listed breakthrough time expires. Accounting for heat, stretching, and physical wear, cutting the listed time in half is a common rule of thumb.
- Dry solids don’t permeate. Permeation only occurs with liquids and gases. A dry powder has no permeation potential, though it can still get through physical openings like holes or loose weaves.
- Thicker isn’t always better. While thicker materials generally provide longer breakthrough times, the right material choice matters far more than thickness. A thin glove made of the correct polymer will outperform a thick glove made of the wrong one.
Employers are responsible for selecting appropriate hand protection based on the specific chemicals and tasks involved. That means consulting the manufacturer’s permeation data, not just grabbing whatever gloves are in the supply closet. If you’re unsure about a particular chemical, the glove manufacturer can provide specific recommendations for safe wear times.