01 May MIL-PRF-85285: Type I vs. Type IV Class H Coatings – Our Comparative Analysis
When you’re producing parts for aerospace and defense OEMs like Boeing, Raytheon, or Lockheed Martin, selecting the right topcoat is non-negotiable. The finish must meet stringent MIL-SPECs—every time. That’s where MIL-PRF-85285 polyurethane coatings come into play. At Royal Coatings, we specialize in helping smaller manufacturers align with prime contractor expectations by offering compliant, high-performance finishes. In this article, we break down the differences between MIL-PRF-85285 Type I and Type IV Class H coatings so you can make informed decisions for your program.
Understanding the Specification
MIL-PRF-85285 is a performance specification developed by the U.S. Department of Defense to govern the use of high-performance polyurethane coatings in demanding aerospace and military environments. It addresses a range of attributes: durability, weather resistance, gloss retention, and chemical resistance, among others. Class H within the spec refers to coatings that are high solids, low VOC (volatile organic compounds), and compliant with current environmental regulations like EPA Rule 1151.
The specification is divided into different Types:
- Type I: Traditional two-component, solvent-based polyurethane.
- Type IV: Advanced high-solids, low-VOC formulation engineered for environmentally regulated environments.
Both fall under Class H, but the differences in their chemistry, application requirements, and field performance can impact your production timeline, cost, and compliance.
Key Differences Between Type I and Type IV Coatings
| Property | Type I (Legacy) | Type IV (Low-VOC, High-Solids) |
| VOC Content | Up to 420 g/L | ≤ 250 g/L |
| Solids Content | ~55–65% | ≥ 70% |
| Application Viscosity | Lower; easier to atomize | Thicker; may require specialized equipment |
| Dry Time | Shorter | Slightly longer |
| Surface Finish | Smooth, uniform | May exhibit more orange peel if not optimized |
| Regulatory Compliance | May be restricted in some states | Fully compliant with strict air quality rules |
| Shelf Life & Storage | Typically stable | Slightly more sensitive to humidity and temperature |
Application and Process Considerations
We see firsthand how coating selection affects shop floor operations. Type I coatings are more forgiving during application and have broader compatibility with existing spray equipment. If you’re working on a legacy program or short production run, Type I may reduce the learning curve.
Type IV, however, requires tighter process controls. Higher viscosity means adjustments to spray equipment and technique—often requiring heated lines or higher-pressure spray guns to atomize the coating properly. It also typically involves longer tack-free times, which can slow production if not accounted for in your schedule.
At Royal Coatings, we’re equipped with enclosed 20′ x 20′ Class A spray booths, high-temp curing ovens, and trained technicians to handle both formulations precisely.
Use Case Recommendations
- Type I is a strong candidate for legacy components, short-run contracts, or programs that haven’t been updated to current environmental standards.
- Type IV is often mandated for new aerospace or military programs, especially in California, where environmental compliance is strictly enforced. If your end customer is located in or shipping through an AQMD-regulated area, Type IV is the safer bet.
We work closely with procurement teams to analyze the program’s Statement of Work (SOW) and align the finish with the required specifications.
Cost, Compliance, and Operational Impact
Type IV coatings often incur higher upfront material costs due to their advanced formulation. However, they can lower your long-term compliance risk, especially if your operation is located in a non-attainment air quality zone.
Operationally, Type IV coatings may extend production time slightly due to longer dry times and more sensitive application requirements. But the trade-off is a modern, regulation-ready finish that meets or exceeds most prime contractor standards.
Whether you’re responding to a QPL callout, prepping for a DLA audit, or just trying to avoid rework, our team helps streamline the path to compliance.
How We Help
We stock both Type I and Type IV Class H MIL-PRF-85285 coatings from QPL-approved manufacturers. Our experience spans military aircraft fuselage components, UAV assemblies, defense enclosures, and satellite hardware. With 50 years of combined expertise and in-house batch ovens, phosphate pretreatment, and Class A booths, we can meet your specs, your timeline, and your budget.
If you’re unsure which type to specify, send us the contract or prime spec sheet. We’ll decode the technical language, cross-reference it with current QPL listings, and recommend the best solution for your production and compliance needs.
Conclusion
Royal Coatings is the trusted partner for aerospace and defense subcontractors across the West Coast for reliable MIL-SPEC coatings and expert-level application support. Let us help you meet specs, stay compliant, and get to market faster.
Contact Royal Coatings today to ensure your next project meets MIL-SPEC standards with precision and speed—trusted experts in aerospace coatings and MIL-PRF-85285.