Moldex 6604 SparkPlugs Uncorded Earplugs NRR 33 200 Pairs Review (2026)

HIGH-DECIBEL WORKPLACES NEED MAXIMUM PROTECTION — DOES THE MOLDEX 6604 DELIVER?

Moldex 6604 SparkPlugs Uncorded Earplugs NRR 33 200 Pairs Review (2026)

At 33 dB NRR, the Moldex 6604 SparkPlugs sit at the practical ceiling of what a single-use foam earplug can legally claim under the ANSI S3.19-1974 test protocol. That ceiling matters. In metal stamping, heavy manufacturing, and high-output construction environments, the difference between 29 dB NRR and 33 dB NRR is the difference between a compliant hearing conservation program and an OSHA 29 CFR 1910.95 citation. This review examines whether the 6604 earns that rating in practice — and whether a 200-pair box purchase makes sense for your operation.

The SparkPlugs line distinguishes itself with vivid multicolor foam: neon green, blue, pink, and yellow rotated through the box. That is not cosmetic. High-visibility hearing protection lets supervisors perform quick visual sweeps of a shop floor to confirm compliance without stopping workers. Moldex engineers this color strategy deliberately, and for safety managers running hearing conservation programs under OSHA 1910.95, that detail matters operationally.

We evaluated the 6604 against its direct competitors in the NRR 33 single-use foam category, cross-referenced the specs against ANSI S3.19 attenuation data, and assessed long-run cost-per-pair economics for bulk buyers. Here is what we found.

Who the Moldex 6604 SparkPlugs Are For

The 6604 is purpose-built for centralized bulk purchasing. It is the right choice for safety managers sourcing disposable hearing protection for manufacturing floors, stamping plants, woodworking shops, or construction staging areas where dispenser infrastructure exists or is planned. Organizations running formal hearing conservation programs under OSHA 29 CFR 1910.95 will find the visual compliance design and maximum NRR rating directly aligned with program requirements. The 200-pair pack structure drives per-pair costs to a level that makes per-use disposal practical without budget pressure.

Individual buyers seeking a quiet commute or sleeping aid will find the SparkPlugs technically capable — NRR 33 is among the highest available — but the bulk packaging and uncorded format are over-engineered for personal use. Those buyers should consider our full earplug collection for individually packaged alternatives.

Strengths of the Moldex 6604 SparkPlugs

NRR 33: What Maximum Attenuation Actually Means

The Noise Reduction Rating of 33 dB is determined under ANSI S3.19-1974 laboratory conditions using human subjects. OSHA and NIOSH both recognize this standard for workplace hearing protection selection. In practice, OSHA's required method for computing effective protection is to derate the NRR: subtract 7 from the NRR, then divide by 2. For the 6604, that yields approximately 13 dB of effective protection. In an 8-hour TWA environment of 95 dBA, the 6604 reduces worker exposure to approximately 82 dBA — comfortably inside OSHA's 90 dBA permissible exposure limit and NIOSH's 85 dBA recommended exposure limit. For environments at or above 100 dBA TWA, dual protection (earplug plus earmuff) is required regardless of NRR. The 6604 performs at the ceiling of what a single earplug device can achieve under this protocol. Learn more in our NRR hearing protection guide.

Allergen-Free Polyurethane Foam Formula

Moldex specifies the 6604 as latex-free, PVC-free, and chloroprene-free. These are meaningful differentiators for workplaces with skin-sensitivity policies or where employees have documented latex or chloroprene allergies. Latex-induced contact dermatitis is a documented occupational health issue, and selecting a latex-free earplug removes that liability without sacrificing attenuation. The polyurethane foam is soft enough to roll down to a slim cylinder for insertion while rebounding consistently to fill the ear canal.

High-Visibility Multicolor for Compliance Management

Safety compliance officers who manage large headcounts benefit from any tool that makes a quick visual sweep meaningful. The SparkPlugs' neon multicolor design — rotating through green, blue, pink, and yellow across pairs in the box — makes plugs immediately visible whether seated in the ear canal or worn around a worker's neck. A supervisor walking a line can visually confirm earplug presence at 5 to 10 feet. This is a measurable operational benefit in high-noise facilities running continuous OSHA 1910.95 monitoring. For deeper insight into compliance frameworks, see our hearing conservation program guide.

Dispenser Ecosystem Compatibility

The 6604 is designed to work within Moldex's dispenser ecosystem — EcoStation, PlugStation, and TouchFree units. For facilities managing dispenser-based PPE distribution, this compatibility means the 6604 plugs directly into an existing Moldex infrastructure without re-procurement of dispensers. TouchFree contactless dispensers are particularly relevant in food processing and pharmaceutical environments where hand hygiene protocols are strict. Explore our full hearing protection collection for compatible products.

200-Pair Box Economics

At 200 pairs per box, the 6604 targets high-volume industrial buyers. The per-pair cost in the 200-pair format is substantially lower than purchasing smaller packs. For operations dispensing earplugs per shift, the math compounds quickly: a 40-person workforce running single daily pairs over a 22-day month consumes 880 pairs, or 4.4 boxes. See our broader analysis of best foam earplugs for budget comparison benchmarks, and best Moldex earplugs for the full Moldex lineup.

Weaknesses of the Moldex 6604 SparkPlugs

Uncorded Format Requires Discipline

Without a cord, the 6604 relies on worker discipline for retention. Plugs removed during breaks can be misplaced, contaminated, or discarded without replacement. In dispenser-equipped facilities this is mitigated — replacements are on hand at every dispenser station — but in field environments without dispensers, uncorded disposables create higher per-unit loss and potential compliance gaps. Facilities where corded hearing protection is preferred should evaluate the Moldex 6654 SparkPlugs corded variant instead.

Insertion Technique is Non-Trivial

Foam earplug effectiveness is technique-dependent. The 6604 requires rolling the plug into a slim cylinder, pulling the ear canal open with the opposite hand, inserting the compressed plug, and holding for 20 to 30 seconds while the foam expands. Workers who insert foam plugs without proper technique will achieve substantially lower real-world attenuation than the labeled NRR 33. OSHA's derating formula partially accounts for this by assuming real-world performance is lower than laboratory results, but technique training remains essential. Any hearing conservation program using foam plugs should include demonstrated insertion as part of onboarding. See our guide to best earplugs for work for technique context.

Not Suited for Intermittent-Noise Work Patterns

Workers who must frequently remove hearing protection to communicate will find repeated disposable earplug removal and reinsertion impractical and unhygienic. Reusable flanged plugs or electronic earmuffs with ambient listening modes are better fits for intermittent-noise patterns. The 6604 is optimized for sustained high-noise exposure where plugs stay in throughout an exposure period. See our earplug collection for reusable alternatives.

No Individual Pair Packaging

Pairs are bulk-packed loose in the box. For facilities distributing hearing protection individually, the loose format creates handling and hygiene considerations versus individually-sealed pairs. See our guide on reusable vs disposable earplugs for a full format comparison.

Competitor Comparison: NRR 33 Foam Earplugs

SparkPlugs Series: Choosing the Right Variant

Accessories and Paired Equipment

The 6604 integrates with Moldex's dispenser lineup. For facilities building or upgrading distribution infrastructure:

• Moldex EcoStation Dispenser — Wall-mount unit designed for bulk earplug pairs; compatible with 6604 format
• Moldex TouchFree Dispenser — Contactless dispensing for hygiene-critical environments (food/pharma)
• Moldex PlugStation — Portable dispenser option for job sites or mobile teams

Browse our full hearing protection collection and PPE catalog for compatible accessories.

OSHA 29 CFR 1910.95 and ANSI S3.19 Context

Under OSHA 29 CFR 1910.95, employers must implement hearing conservation programs when workers are exposed to an 8-hour time-weighted average of 85 dBA or higher. Hearing protection must be provided when TWA reaches 90 dBA or when employees have experienced standard threshold shifts. The regulation mandates that provided hearing protection reduce exposure to 90 dBA or below (or 85 dBA for employees with threshold shifts).

The NRR is established under ANSI S3.19-1974 using real-ear-at-threshold (REAT) methodology with trained laboratory subjects. Because laboratory conditions overestimate real-world performance, OSHA requires an NRR derating: subtract 7 from the NRR, divide by 2. For the 6604 (NRR 33): (33 - 7) / 2 = 13 dB of effective protection. A worker in a 103 dBA environment using properly fitted 6604 SparkPlugs receives 103 - 13 = 90 dBA effective exposure — exactly at the OSHA PEL for an 8-hour TWA. Environments above 103 dBA TWA require dual protection or alternative controls. For a full breakdown, see our NRR hearing protection guide and hearing conservation program guide.

Total Cost of Ownership: The 200-Pair Economics

Disposable earplug programs have predictable cost structures. The 200-pair box format is the baseline for serious industrial buyers. A 50-worker facility issuing one fresh pair per shift, five days a week, consumes approximately 1,100 pairs per month — about 5.5 boxes. Annualized, that is roughly 13,200 pairs or 66 boxes per year.

Dispenser infrastructure carries a one-time capital cost but reduces per-unit waste and handling time. Facilities investing in Moldex EcoStation or TouchFree units typically recover the dispenser cost through reduced per-pair waste over 6 to 12 months of deployment. Compare total-program approaches in our guide to reusable vs disposable earplugs and the best hearing protection guide.

Final Verdict

The Moldex 6604 SparkPlugs earn their 4.7/5 rating by delivering on the three criteria that matter most to industrial hearing protection buyers: maximum NRR attenuation, an allergen-free foam formula that keeps HR liability low, and a visual design that makes compliance monitoring practical at scale. The 200-pair bulk format prices well for high-volume procurement, and dispenser ecosystem compatibility adds operational value for facilities already invested in Moldex infrastructure.

The weaknesses are real but contextual: uncorded format and loose bulk packaging are limitations only in environments without dispenser infrastructure or where workers lack plug-insertion training. Address those two factors and the 6604 is a strong default choice for any NRR 33 foam earplug program. Facilities with food or pharmaceutical contamination mandates should specify the 6615 metal-detectable variant instead.

For general industrial, construction, and manufacturing hearing conservation programs, the Moldex 6604 SparkPlugs are a top-tier recommendation. See our roundup of the best earplugs for work and best Moldex earplugs for further context.

Frequently Asked Questions

What is the NRR of the Moldex 6604 SparkPlugs?

The Moldex 6604 SparkPlugs have a Noise Reduction Rating of 33 dB, tested and certified under ANSI S3.19-1974. This is the maximum NRR achievable in the single-use foam earplug category.

How does OSHA derating affect the 6604 real-world protection?

OSHA requires derating: (NRR 33 - 7) / 2 = approximately 13 dB effective protection. In a 95 dBA TWA environment, properly fitted 6604 plugs reduce effective exposure to approximately 82 dBA — below both OSHA's 90 dBA PEL and NIOSH's 85 dBA REL. In a 103 dBA TWA environment, estimated effective exposure is 90 dBA, the OSHA PEL boundary.

Are the Moldex 6604 SparkPlugs latex-free?

Yes. The 6604 is made from polyurethane foam and is specified as latex-free, PVC-free, and chloroprene-free. This makes them suitable for workplaces with latex sensitivity or allergy policies.

How do I insert foam earplugs correctly to get full NRR 33 protection?

Roll the earplug into a slim cylinder. With the opposite hand, pull the ear canal open by gently tugging the top of the outer ear upward and back. Insert the rolled plug and hold for 20 to 30 seconds while the foam expands. Proper technique is critical — improperly inserted foam plugs can perform far below labeled NRR.

What is the difference between the Moldex 6604 and the 6654?

The 6604 is uncorded and comes in 200-pair boxes. The 6654 is the corded version, sold in 100-pair boxes. Both have NRR 33 and the same multicolor polyurethane foam. The cord on the 6654 connects the two plugs so they hang around the neck when not in use, reducing loss risk.

Can the Moldex 6604 be used in food processing environments?

The 6604 itself is not metal-detectable. Food processing or pharmaceutical facilities operating under HACCP, BRC, or SQF programs requiring detectable hearing protection should use the Moldex 6615 SparkPlugs metal-detectable corded variant instead.

How many pairs are in a box of Moldex 6604?

Each box contains 200 pairs (400 individual earplugs) bulk-packed without individual wrapping.

Are the Moldex 6604 SparkPlugs compatible with Moldex dispensers?

Yes. The 6604 SparkPlugs are compatible with Moldex EcoStation, PlugStation, and TouchFree dispenser units, making them suitable for organized facility-wide distribution programs.

Why are the SparkPlugs multicolored?

The vivid multicolor design — rotating through neon green, blue, pink, and yellow — provides high visibility so safety supervisors can visually confirm earplug use on a shop floor without requiring workers to stop. This is an intentional compliance-monitoring design feature, not cosmetic.

Can the Moldex 6604 be reused across shifts?

The 6604 is classified as a disposable single-use earplug. For planned reuse programs, reusable flanged earplugs are a better fit. See our guide on reusable vs disposable earplugs.

What noise levels require NRR 33 earplugs?

Using OSHA's derating formula, NRR 33 earplugs provide approximately 13 dB of effective protection, appropriate for sustained exposures up to approximately 103 dBA TWA when used alone. Above that level, dual protection (earplug plus earmuff) is required.

How do the Moldex 6604 SparkPlugs compare to 3M 1100 earplugs?

The 3M 1100 has NRR 29 versus NRR 33 for the 6604. For high-noise environments requiring maximum attenuation, the 6604 provides more headroom. The 6604 also carries the allergen-free (latex/PVC/chloroprene-free) specification and the high-visibility multicolor design.

Do the Moldex 6604 SparkPlugs meet OSHA hearing conservation requirements?

Yes. The 6604 is designed to meet OSHA 29 CFR 1910.95 hearing conservation standards. When properly fitted in appropriate noise environments up to approximately 103 dBA TWA for single protection, the 6604 provides attenuation adequate for OSHA compliance. Employers must verify adequacy via the OSHA derating calculation for their specific TWA exposures.

What is the best way to distribute Moldex 6604 earplugs in a large facility?

Moldex dispenser systems — EcoStation (wall-mount), PlugStation (portable), and TouchFree (contactless) — are designed for facility-wide bulk earplug distribution. The 200-pair box refill format is sized for dispenser refilling. Dispenser-based distribution reduces per-unit waste, simplifies restocking, and provides consistent access points throughout a facility.

Are Moldex earplugs made in the USA?

Moldex-Metric is a US-based manufacturer headquartered in Culver City, California. Specific facility sourcing for individual SKUs should be confirmed with Moldex directly for compliance or procurement documentation purposes.

Where can I buy Moldex 6604 SparkPlugs in bulk?

The Moldex 6604 SparkPlugs 200-pair box is available directly from WC Safety and from Amazon. For larger facility orders, contact WC Safety directly.

How does the Moldex 6604 fit workers with small ear canals?

The SparkPlugs are available in one size. The roll-down foam design accommodates a range of ear canal sizes because the foam compresses for insertion and then expands to fill the available space. Workers with very small ear canals who experience difficulty achieving a seal should trial the Moldex Pura-Fit 6800 series, which features a tapered body that may offer easier insertion.

Reviewed by Steven Eaton — Safety Professional, WC Safety | Hearing Protection Specialist | WC Safety Editorial Team

Steven Eaton has over a decade of experience in occupational safety product selection and has evaluated hearing protection for OSHA 1910.95 compliance programs across manufacturing, construction, and food processing sectors.

Review Methodology

This review is based on product specifications published by Moldex-Metric, ANSI S3.19-1974 attenuation test methodology, and OSHA 29 CFR 1910.95 regulatory requirements. NRR derating calculations apply OSHA's required method. Competitor NRR values are sourced from manufacturer documentation. No independent laboratory testing was conducted by WC Safety for this review. All internal links point to verified live WC Safety pages.