Moldex 6604 Sparkplugs Review
WC Safety Editorial Verdict: 4.5/5
WC Safety Editorial Verdict — 4.5 / 5. The Moldex 6604 SparkPlugs is the format we recommend first when the goal is the highest NRR available in a disposable roll-down plug paired with reliable insertion: the dual-layer firm-skin-over-soft-core build makes the roll-down step achievable with sweaty or gloved hands, and the 200-pair uncorded box is the correct primary-dispensing SKU. We score it editorially against the rest of the foam ear plugs range rather than on customer counts — at NRR 33 it sits at the top of the high-NRR ear plugs tier, but remember NIOSH derates foam by ~50%, so plan for roughly 17–18 dB of real-world reduction.
Skip it only if you need a cord for FOD control (see the Moldex 6654 SparkPlugs corded), metal-detectability for food or pharma (the Moldex 6615 metal detectable), or a softer single-layer feel (Moldex 6800 Pura-Fit).
Moldex 6604 SparkPlugs Earplugs Review: NRR 33 Uncorded Dual-Layer Foam — 200-Pair Box for High-Noise Industrial Environments
Published · Last updated
The Moldex 6604 SparkPlugs is the standard uncorded bulk-pack format of Moldex's dual-layer foam earplug — NRR 33, 200 pairs per box, made in the USA, carrying the EPA-required NRR label (40 CFR Part 211) tested per ANSI/ASA S3.19. For the corded variant, see the Moldex 6654. For metal-detectable corded, see the Moldex 6615. For a 500-pair workstation jar, see the Moldex 6684. If you need a softer foam feel at NRR 33, see the Moldex 6800 Pura-Fit or Moldex 6600 Softies.
Editorial Verdict — 4.5 / 5
The 6604 anchors the Moldex SparkPlugs family at NRR 33 in a dual-layer foam construction that makes consistent roll-down insertion achievable across a wider range of hand conditions than single-layer foam earplugs. The 200-pair bulk box is the correct format for primary workstation dispensing. Corded (6654), metal-detectable (6615), and jar (6684) variants cover all deployment scenarios.
Quick-Reference Specs: Moldex 6604 SparkPlugs
| Specification | Detail |
|---|---|
| Model | 6604 |
| NRR | 33 dB (ANSI/ASA S3.19) |
| NIOSH Effective Exposure Reduction | NRR 33: (33 − 7) ÷ 2 = 13 dB effective reduction under the enforcement estimate |
| Format | Uncorded, roll-down foam |
| Construction | Dual-layer: firm outer skin / soft expanding foam core |
| Pack Size | 200 pairs per box |
| OSHA Standard | 29 CFR 1910.95 (Hearing Conservation) |
| Country of Origin | USA |
| Related Variants | 6654 (corded), 6615 (metal-detectable corded), 6684 (500-pair jar) |
Understanding the SparkPlugs NRR 33 Rating
The Moldex SparkPlugs 6604 carries an NRR of 33, the same top foam rating as the Pura-Fit 6800 and Softies 6600. Under OSHA 29 CFR 1910.95, NRR is used to estimate worker exposure by subtracting a derated NRR value from the measured environmental noise level. NIOSH recommends derate by 50% (multiply NRR by 0.5) for foam earplugs based on real-world fit studies.
Derating calculation comparison:
| Earplug | Labeled NRR | Derated estimate ((NRR − 7) ÷ 2) | Effective Reduction (dB) | Protected at 110 dB TWA? |
|---|---|---|---|---|
| Moldex 6604 SparkPlugs | 33 | (33 − 7) ÷ 2 = 13 | ~13 dB | No — 110 − 13 = 97 dBA (exceeds PEL; plan dual protection) |
| Moldex 6800 Pura-Fit | 33 | (33 − 7) ÷ 2 = 13 | ~13 dB | No — 110 − 13 = 97 dBA (exceeds PEL) |
| Moldex 6600 Softies | 33 | (33 − 7) ÷ 2 = 13 | ~13 dB | No — 110 − 13 = 97 dBA (exceeds PEL) |
| Generic NRR 29 earplug | 29 | (29 − 7) ÷ 2 = 11 | ~11 dB | No — 110 − 11 = 99 dBA (exceeds PEL) |
Moldex publishes NRR 33 for the 6604 — the same top rating as its foam peers, with no additional margin over other NRR 33 plugs. Under OSHA's enforcement estimate (TWA − (NRR − 7) ÷ 2), the 6604's NRR 33 provides the same 13 dB credited reduction as its NRR 33 peers.
Dual-Layer Construction: Why SparkPlugs Inserts More Reliably
The defining characteristic of the SparkPlugs design is its dual-layer construction — a firmer outer skin layer over a soft expanding foam core. Standard single-layer foam earplugs (including Pura-Fit and Softies) require workers to roll the entire plug to a small enough diameter for insertion, which is difficult with sweaty, dirty, or gloved hands. The SparkPlugs outer skin provides a grab surface that compresses the inner foam when rolled, making the roll-down technique more achievable under field conditions.
This construction difference directly affects compliance rates. OSHA 29 CFR 1910.95(i)(4) requires that hearing protectors be worn continuously during noise exposure — a requirement that depends heavily on whether workers find the insertion process practical. The SparkPlugs' easier roll-down addresses one of the primary behavioral barriers to consistent earplug use in construction, manufacturing, and aviation environments.
Insertion Instructions for Maximum NRR 33 Performance
Correct insertion technique is essential for achieving the labeled NRR. Under ANSI/ASA S3.19, NRR is measured in a controlled laboratory setting with proper insertion. Real-world performance depends entirely on consistent insertion technique:
- Clean hands: Wash or sanitize hands before handling earplugs — contamination reduces foam expansion.
- Roll down: Using the SparkPlugs' firm outer skin, roll the plug between thumb and index finger to compress it to the smallest possible diameter. The dual-layer construction makes this step easier than single-layer foam.
- Pull ear up and back: With the opposite hand, reach over the head and pull the outer ear (pinna) up and back to straighten the ear canal.
- Insert deeply: While holding the ear pulled, insert the rolled plug deeply into the canal — the tip of the plug should sit at the canal entrance, not merely at the bowl of the ear.
- Hold for 30–60 seconds: Continue holding the plug in place while the foam expands to fill and seal the canal. Release only after expansion is complete.
- Check fit: In a noisy environment, a well-inserted earplug should reduce sound to a noticeably muffled level. If not, remove, re-roll, and reinsert.
OSHA 29 CFR 1910.95 Hearing Conservation Requirements
OSHA's Hearing Conservation Amendment (29 CFR 1910.95) requires employers to implement hearing conservation programs when worker TWA noise exposure reaches or exceeds the action level of 85 dBA. Requirements include noise monitoring, audiometric testing, hearing protection provision, training, and recordkeeping. Key thresholds:
- Action level: 85 dBA TWA — hearing conservation program required
- PEL: 90 dBA TWA — engineering controls and hearing protection required
- 115 dBA instantaneous — never permissible without hearing protection
- 140 dBA peak impulse — ceiling, never permissible
For operations where noise levels reach 110 dBA TWA or higher — common in stamping, press operations, grinding, and aviation — the 6604's NRR 33 matches the highest protection available in a disposable foam earplug format.
Industries and Applications for the Moldex 6604
The 6604 is appropriate across a wide range of high-noise industries:
- Manufacturing / Heavy Industry: Press rooms, stamping, grinding, metalworking where 105–115 dBA TWA is common
- Construction: Jackhammers, compactors, concrete saws, powered nailers — OSHA 29 CFR 1926.52 construction noise standard applies
- Aviation / Ground Support: Ramp operations near jet engines; NRR 33 is the top foam rating specified for jet noise environments
- Utilities / Power Generation: Turbine halls, compressor stations, generator rooms exceeding 100 dBA
- Pulp and Paper / Saw Mills: Head rigs, chippers, debarkers generating 105+ dBA
SparkPlugs Family Comparison: Choosing Between 6604, 6654, 6615, and 6684
| Model | NRR | Format | Pack Size | Best For |
|---|---|---|---|---|
| 6604 | 35 | Uncorded, bulk box | 200 pairs | Primary workstation dispensing — highest NRR |
| 6654 | 35 | Corded | 100 pairs | FOD-prevention and cord-mandate facilities |
| 6615 | 35 | Corded + metal-detectable | 100 pairs | Food processing, pharma — HACCP X-ray detection |
| 6684 | 35 | Uncorded, workstation jar | 500 pairs | Secondary workstations, toolboxes, no dispenser |
Browse the full hearing protection collection at WC Safety for dispensers, earmuffs, and complete hearing conservation program supplies.
Frequently Asked Questions: Moldex 6604 SparkPlugs
Q: What is the NRR of the Moldex 6604 SparkPlugs?
A: NRR 33, per Moldex's published specification, measured per ANSI/ASA S3.19 in laboratory conditions. The derated estimate — (33 − 7) ÷ 2 — yields approximately 13 dB of effective noise reduction under typical field conditions.
Q: What is dual-layer earplug construction and why does it matter?
A: The 6604 SparkPlugs uses a firmer outer skin over a soft expanding foam core. This dual-layer design makes the roll-down insertion step easier than single-layer foam earplugs, especially when hands are sweaty, dirty, or gloved. Easier insertion leads to better compliance with OSHA 29 CFR 1910.95 continuous wear requirements during noise exposure.
Q: Does the SparkPlugs NRR 33 give an edge for OSHA compliance?
A: No — the 6604 is itself NRR 33. Under OSHA's enforcement estimate ((33 − 7) ÷ 2) it provides about 13 dB of credited reduction, identical to other top foam plugs.
Q: Is the 6604 NIOSH approved?
A: No — NIOSH approval under 42 CFR Part 84 covers respirators, not earplugs. The 6604 carries the EPA-required NRR label (40 CFR Part 211): NRR 33, tested per ANSI/ASA S3.19, which OSHA accepts for hearing conservation program documentation.
Q: What OSHA standard governs earplug use in manufacturing?
A: OSHA 29 CFR 1910.95 (Occupational Noise Exposure) for general industry. For construction, 29 CFR 1926.52 applies. Both standards require hearing protection when TWA noise exceeds the PEL (90 dBA) or — under 1910.95's hearing conservation amendment — when the action level (85 dBA) is reached.
Q: When should I choose the 6604 over the corded 6654?
A: Choose the uncorded 6604 for workstations where cord-mandate policies do not apply and where the primary concern is maximum NRR at the lowest per-pair cost. Choose the corded 6654 when a facility FOD-prevention policy, HACCP cord mandate, or operational requirement prohibits loose earplugs that could fall into product or machinery.
Q: What is the difference between the 6604 and the 6684 workstation jar?
A: Both contain the same SparkPlugs NRR 33 foam — same protection, same insertion technique. The 6684 comes in a 500-pair lidded jar for open-access workstation dispensing without individual wrappers. The 6604 comes in a 200-pair bulk box with individually wrapped pairs for dispensing via a dispenser unit. The 6604 bulk box is the primary source for refilling dispensers; the 6684 jar is for secondary workstations too small for a dispenser.
Q: Can the 6604 be used in food processing environments?
A: The 6604 is not metal-detectable — for food processing and pharmaceutical environments requiring HACCP compliance with X-ray or metal detection programs, use the 6615 metal-detectable corded variant. The 6604 is appropriate for non-HACCP manufacturing environments.
Q: How should the 6604 be disposed of?
A: The 6604 SparkPlugs is a single-use disposable earplug. Do not wash and reuse — the foam's expansion characteristics degrade significantly after the first use cycle. Dispose of used plugs in regular trash unless the work environment involves hazardous materials that require special disposal protocols (e.g., lead-contaminated earplugs from a firing range).
Q: What is the APF (Assigned Protection Factor) for earplugs?
A: NIOSH does not assign APF values to hearing protectors the same way OSHA assigns APFs to respirators. Instead, NIOSH provides expected protection value guidance based on derated NRR. In practice the NRR 33 SparkPlugs provides approximately 13 dB of effective protection using NIOSH 50% derating — the maximum achievable in a disposable foam earplug format.
Q: Is the Moldex 6604 made in the USA?
A: Yes. Moldex manufactures SparkPlugs earplugs in the United States. Moldex is one of the few major earplug manufacturers that produces all its foam earplug products domestically.
Q: How does the SparkPlugs compare to the Pura-Fit for workers who find insertion difficult?
A: The SparkPlugs (6604) has a firmer outer layer that makes roll-down easier — it is the better choice for workers who find soft single-layer foam (like the Pura-Fit 6800) difficult to grip and roll thin enough. However, some workers with sensitive ear canals find the firmer outer skin less comfortable after hours of wear — for them, the ultra-soft Pura-Fit or Softies may be preferred at the expense of 2 dB of NRR.
Q: What dispensers are compatible with the Moldex 6604?
A: The 6604 200-pair bulk box is compatible with Moldex's EcoStation dispensers and standard pilfer-proof earplug dispenser cabinets. See the WC Safety hearing protection collection for compatible Moldex dispenser options.
Q: Does wearing earplugs affect communication and situational awareness?
A: Yes — NRR 33 earplugs significantly reduce ambient sound, which can affect communication and awareness of warning signals. OSHA 29 CFR 1910.95(i)(3)(iii) requires that hearing protectors not interfere with the ability to hear warning signals. Hearing protectors with flat attenuation or electronic earplugs with pass-through audio may be appropriate for environments with critical communication requirements. For standard high-noise operations, train workers on the specific warning signals used and verify they remain audible with hearing protection worn.
Q: Where can I buy the Moldex 6604 SparkPlugs?
A: reviewed at WC Safety in the 200-pair bulk box format, or check Check Price on Amazon → for price comparison. Browse the full hearing protection collection at WC Safety including all SparkPlugs variants and competing foam earplug options.
Disclosures & editorial standards
WC Safety participates in the Amazon Services LLC Associates Program. Outbound Amazon links are affiliate links. We accept no manufacturer payment, sponsorship, or product samples. This content is not medical, legal, or regulatory advice. Safety equipment selection is governed by applicable OSHA standards and your facility's safety program.
WC Safety participates in the Amazon Services LLC Associates Program. Outbound Amazon links are affiliate links. We accept no manufacturer payment, sponsorship, or product samples. This content is not medical, legal, or regulatory advice. Safety equipment selection is governed by applicable OSHA standards and your facility's safety program.
Pros & Cons
Pros
- NRR 33 — the top of the disposable foam tier, shared with the best competing plugs, with solid derating headroom under OSHA 1910.95
- Dual-layer construction (firm outer skin over soft expanding core) makes roll-down insertion more reliable with sweaty, dirty, or gloved hands than single-layer foam
- 200-pair uncorded bulk box is the correct economical format for refilling primary workstation dispensers
- NIOSH approved under 42 CFR Part 84, rated per ANSI/ASA S3.19, and made in the USA
- Individually wrapped pairs keep plugs clean for hand-out dispensing and meet hygiene expectations in food-adjacent (non-HACCP) areas
- Same NRR 33 foam carries across corded, metal-detectable, and jar variants, so one brand standard covers every deployment scenario
Cons
- Single-use only — the foam's expansion characteristics degrade after the first cycle, so unlike reusable flanged plugs it cannot be washed and reused
- Uncorded, so it offers no FOD/contamination control where a cord mandate applies — the 6654 or 6615 is required in those facilities
- Not metal-detectable, ruling it out for HACCP food-processing and pharmaceutical lines that run metal/X-ray detection
- Firmer outer skin can feel less comfortable than ultra-soft single-layer foam over a full shift for workers with sensitive ear canals
- Only a 2 dB labeled-NRR edge over NRR 33 plugs — after NIOSH derating that narrows to ~1 dB of real-world difference
Who It's For
Buy it if:
- Safety managers stocking a primary earplug dispenser in high-noise plants (stamping, grinding, press rooms) at 105–115 dBA TWA
- Operations needing the maximum NRR available in a disposable roll-down format for OSHA 1910.95 / 1926.52 compliance
- Workers who struggle to roll single-layer foam thin enough and benefit from the firmer dual-layer grab surface
- Buyers who want the lowest per-pair cost in bulk and do not need a cord or metal detection
- Aviation ground-support and utility crews where NRR 33 is the standard jet-noise/turbine-hall specification
Look elsewhere if:
- Food-processing and pharma teams under HACCP metal/X-ray detection — choose the metal-detectable 6615 instead
- Facilities with a cord/FOD mandate that prohibit loose plugs — choose the corded 6654
- Workers wanting a washable, reusable plug rather than a single-use disposable — look at flanged reusable earplugs
- Anyone prioritizing all-day softness over the last 2 dB of NRR, who may prefer the ultra-soft Pura-Fit or Softies
Related Resources
- foam ear plugs
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- moldex 6604 sparkplugs
- moldex 6654 sparkplugs corded
- moldex 6615 sparkplugs metal detectable
- moldex 6684 sparkplugs jar
- moldex 6800 pura fit
- moldex 6900 pura fit corded
- moldex 6600 softies
- moldex 6650 softies corded
Common questions
Sources. Requirements referenced here come from OSHA 29 CFR 1910 and the NIOSH recommendations. Where a consensus standard governs, the ANSI document is named in the text.
Related reference
Related on this site: 3m 1100 foam ear plugs, cordless (uncorded) - nrr 29, 200-pair box, 3m 1110 foam earplugs nrr 30 200 pairs, moldex pura-fit vs howard leight max-1: which nrr 33 ear plug?, what is nrr noise reduction rating explained, best metal detectable ear plugs, and highest nrr ear plugs (2026): 7 best nrr 33 picks ranked.
Why trust WC Safety
WC Safety is an independent, affiliate-supported review site. It is not a retailer: it holds no inventory, takes no orders, and earns only from qualifying purchases through clearly marked links — which never changes what a product is rated to do. Standards language is taken from the regulation text directly, and ratings are reported as the manufacturer publishes them. We run no laboratory and perform no testing of our own. Where published sources disagree, we say so and plan on the conservative figure rather than the flattering one.
Our methodology
Figures come from the regulation and the published specification, in that order. Derated numbers are calculated, not estimated. Nothing here is presented as a measured result, because we measure nothing.
Researched and written by Steven Eaton, editor of WC Safety. Steven holds no safety certification and does not test products; this page compares what manufacturers and regulators publish, with the gaps in that record marked. Last reviewed August 2026.
Affiliate disclosure: as an Amazon Associate, WC Safety earns from qualifying purchases. WC Safety is not a retailer and takes no orders — links go to the seller, and the price you pay is unchanged.
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