If you've ever stood in a sporting goods aisle trying to decide between two pairs of earplugs, you've probably looked at the NRR on the label and assumed the higher number wins. It's a reasonable instinct. But if you're a hunter or shooter, that number may be telling you very little about the protection you will actually receive.
Here's why, and what to look for instead.
What Is the NRR?
NRR stands for Noise Reduction Rating. It is the standard hearing protection label required by the U.S. Environmental Protection Agency (EPA) for devices sold in the United States.
The NRR is determined through controlled laboratory testing using low-level sounds. A listener's hearing threshold is measured with and without the hearing protector in place, and the difference between those thresholds is used to calculate attenuation.
The key detail is this: NRR testing is conducted using relatively low-level, steady-state sounds, well below the intensity of real-world impulse noise such as firearms. Within that range, hearing protection behaves in a largely linear way, meaning attenuation remains relatively consistent across the levels being tested. That is the performance the NRR reflects.
What it does not reflect is how a device performs against high-level impulse noise.
Why the NRR Falls Short for Firearm Noise
This is where most people are misled.
At the extreme peak levels produced by firearms, hearing protection behaves differently than it does in low-level laboratory conditions. Attenuation is non-linear, meaning it changes depending on the intensity of the impulse. In many cases, protectors provide greater attenuation at higher impulse levels.
Because the NRR is calculated at the opposite end of this nonlinear range, it does not capture this behavior.
Recreational shooters and law enforcement personnel are routinely exposed to impulse peaks between 150 and 170 dB SPL. Research and manufacturer data consistently show that there is no reliable relationship between NRR values and impulse performance under these conditions.
Using NRR to evaluate hearing protection for shooting is similar to using a car's city fuel economy rating to judge highway performance. It measures the same general concept under conditions that do not translate.
All Ratings Assume an Ideal Fit
Before comparing rating systems, there is one principle that applies across all of them.
Every rating, whether NRR, IPIL, SNR, or any other system, is generated in a laboratory by trained personnel fitting the device under controlled conditions according to manufacturer instructions. The number on the package reflects performance when everything is done correctly.
In the real world, that level of fit is rarely achieved.
Insertion depth, ear canal anatomy, device movement, and lack of instruction all reduce real-world protection. A product's rating describes what it is capable of. What you receive depends on whether it is fitted correctly.
This is the foundation of OtoPro's approach. Custom earmold impressions, taken through a clinically guided process and matched to the anatomy of your ear, remove the largest variable in hearing protection performance. The process is not separate from the product. The process is the product.
Continuous Noise: Where NRR Applies
For environments involving continuous noise, such as manufacturing, aviation, concerts, or power tools, the NRR is the appropriate starting point. However, real-world performance is consistently lower than labeled values, which is why NIOSH recommends derating.
Derating varies by protector type:
- Earmuffs: subtract 25%
- Formable foam earplugs: subtract 50%
- Premolded and other earplugs: subtract 70%
For example, a foam earplug with an NRR of 33 provides approximately 16 to 17 dB of real-world protection after derating. A premolded earplug with the same NRR provides closer to 10 dB.
These adjustments apply only to continuous noise. They should not be used to estimate protection from impulse noise such as gunfire.
At OtoPro, we offer a number of acoustic filters which use steady NRR ratings. Our Fidelity Filter, for example, provides the most even attenuation from bass to treble. This allows for the overall volume to decrease without a concert sounding muffled.
Gunshot Noise: Where IPIL Applies
IPIL stands for Impulsive Peak Insertion Loss. It is the measurement designed specifically for high-level impulse environments such as firearms.
IPIL is measured by exposing the hearing protector to high-level impulse sounds that simulate firearm noise and then calculating the reduction in peak level. Under ANSI testing, this is typically done at multiple peak levels. Because attenuation changes with intensity, results are ideally reported at each level rather than as a single number.
In practice, however, you will often see a single IPIL value reported. This is usually derived from testing at a specific impulse level (commonly around 150 to 160 dB peak SPL) and expressed as the amount of reduction in decibels. For example, an IPIL of 33 dB means a 160 dB impulse is reduced to approximately 127 dB at the ear. This simplified value is useful, but it does not fully capture how performance may change at higher or lower impulse levels.
A key point: IPIL values are often higher than a device's NRR.
This reflects the non-linear behavior of hearing protection. A passive filtered earplug with a low NRR may still deliver substantial impulse attenuation. Likewise, electronic devices may provide strong impulse protection even when their NRR appears modest.
This is what makes NRR misleading for shooters. The only number on the package can make a highly effective product appear inadequate, while offering no insight into how it performs in the environment it is actually used.
Field research has demonstrated that impulse attenuation increases as peak level increases, reinforcing that impulse performance cannot be inferred from NRR.
Despite this, IPIL is not currently required on product labeling, leaving most consumers without access to the most relevant metric for shooting applications.
An example of IPIL within the current OtoPro catalog is our popular Impulse Filter. The Impulse filter allows soft sounds to pass through with barely perceptible attenuation, so its NRR is only about 5 dB. The membrane inside the filter dynamically changes in response to the nonlinear nature of sound pressure, becoming completely stiff at the impulse blast of a gunshot. The IPIL rating for this filter is 33.1 dB. This allows shooters to hear low-level sounds and be protected from the gunshot instantaneously.
What About SNR and Other Systems?
International products may use different rating systems, but they share the same underlying limitation.
SNR (Single Number Rating), used in Europe, is comparable to NRR in that it measures continuous noise attenuation under laboratory conditions. It is calculated differently and is not directly interchangeable with NRR, but it does not address impulse noise.
Some systems also report frequency-specific values, which can be useful in industrial settings. Others, such as SLC80, present more conservative estimates based on population performance. Assigned Protection Factors (APF) are used in occupational safety to estimate expected protection under supervised use.
None of these systems evaluates impulse noise. For firearm exposure, IPIL remains the appropriate metric.
The Bottom Line
Every rating system describes what a hearing protector can do under ideal conditions. The number on the package is a starting point, not a guarantee.
Across all scenarios, fit is the dominant variable. A precisely fitted device with a lower rating will outperform a poorly fitted device with a higher one. The goal is not just to buy protection, but to ensure it is performing the way it was designed to.
That is where a clinical process matters. When fit is dialed in, you are no longer guessing whether the product is working. You can trust that it is.
If you are unsure whether your current protection is appropriate for your environment, that is a conversation worth having. You can reach us through the contact tab on our website or at info@otoprotechnologies.com.
Grace Sturdivant, Au.D., CCC-A is the founder of OtoPro Technologies. OtoPro provides individualized hearing protection and custom-fitted solutions for hunters, competitive shooters, musicians, and individuals in occupational noise environments.