Spec It Right in 2025: Choosing Durability Tests for Optical Filters—MIL-C-48497A or ISO 9211?
Choosing the right durability standard for optical filters can make or break the reliability of your product—especially in military, aerospace, or high-demand industrial environments. In 2025, the most asked question remains: should you specify legacy MIL-C-48497A or the modular, modern ISO 9211? Here is how to spec it right.
The Legacy Option: MIL-C-48497AMIL-C-48497A is a legacy U.S. military specification defining minimum durability for single- and multilayer interference optical coatings (like AR and basic thin-film stacks). Its main tests:
- Adhesion: Tape pull test (cellophane tape pressed on and peeled off the coating, must not lift)
- Humidity Exposure: 120°F (49°C) at 95-100% relative humidity
- Moderate Abrasion: Cheesecloth rub (defined cycles/pressure)
- Temperature Cycling: -80°F to +160°F in sequence
- Solvent Resistance: Tested with common solvents (like acetone, alcohol), checking for damage
It's inactive for new designs as of 1997, but still turns up in U.S. defense contracts and many legacy programs. If a customer asks for it, you must comply or offer a clear ISO mapping.
The Modern Solution: ISO 9211 SeriesISO 9211 is the go-to international suite covering both optical and durability specifications:
- ISO 9211-1: Defines all the key vocabulary
- ISO 9211-2 (2024): Tells you how to specify optical properties (T/R over a band, blocking, graphs)
- ISO 9211-3 (2024): Defines categories of use and which ISO 9022 environmental durability tests are required for your application
- ISO 9211-4 (2022): Specifies detailed methods for abrasion, adhesion (tape peel/crosshatch test), and water/solvent resistance
ISO spec notation is concise: Drawings list codes for performance and each test, plus severity, so suppliers know exactly what to do.
How Do They Compare?| Test Type | MIL-C-48497A | ISO 9211 (2024) |
|---|---|---|
| Adhesion | Tape pull | ISO 9211-4 crosshatch/peel, tape force defined |
| Abrasion | Cheesecloth (moderate) | ISO 9211-4 abrasion, length/load specified |
| Temp/Humidity | -80 to +160°F, 120°F/95-100% RH | ISO 9211-3/ISO 9022, severity per application |
| Solvent/Chemical | Common solvents, acceptance visual | ISO 9211-3 category + chemicals specified |
Option A — ISO-only (recommended for new work)
Use ISO 9211-2 to specify optical properties and ISO 9211-3/-4 (plus ISO 9022) to define durability and environmentals. List all tests & severities on the drawing, e.g.:
- Humidity (ISO 9022), severity per application
- Abrasion (ISO 9211-4), load & cycles stated
- Adhesion—tape peel (ISO 9211-4, tape ≥ 9.8 N/25 mm)
- Water immersion (ISO 9211-4)
- All tests on a single witness sample (sequentially), unless otherwise specified
Option B — Legacy MIL (for U.S. defense or legacy contracts)
Keep 'Durability per MIL-C-48497A' in your drawing and detail optical properties separately (preferably with ISO notation). Add a note that MIL-C-48497A is inactive for new designs. For best practice, prepare an ISO mapping table for documentation and supplier QA review.
Option C — Hybrid (for smooth procurement/legacy bridge)
Specify all optical/durability as per ISO, plus:
This approach reassures legacy defense customers while keeping modern practice and clarity for suppliers and QA.
When Should You Use Each?- New commercial/dual-use optics: ISO 9211 only. Globally recognized, clear, and modular.
- U.S. defense projects with MIL callouts: Stick with MIL-C-48497A for acceptance/contract, but use ISO mapping for suppliers and internal QA.
- Procurement peace of mind: Hybrid—ISO for all, MIL for legacy acceptance.
- ISO 9211 is best for clarity, current practice, and international acceptance. MIL-C-48497A lingers in defense due to legacy, but mapping to ISO codes keeps your specs robust, audit-ready, and understandable for global suppliers.
- Spec it right for long-term durability and customer satisfaction!
