If you’ve looked closely at a material data sheet (access the Atlas Fibre 2026 Resource Kit), you may have noticed a line referencing an ASTM test method, sometimes followed by a short string of numbers and letters – something like “96/23/50.” These aren’t arbitrary codes. They describe exactly how the test specimen was prepared before testing, and that detail matters more than it might seem.
Why Conditioning Matters
Temperature and humidity change how plastics and composites behave. A laminate tested right after molding, while it still holds residual moisture or heat, can produce different mechanical or electrical results than the same material tested after it has stabilized at room conditions. Neither result is “wrong” – they’re just answers to different questions.
To make results comparable across labs, suppliers, and time, the industry standardizes how specimens are conditioned before and during testing. For laminated thermosetting materials specifically, that standard is ASTM D709. When a data sheet cites a conditioning code, it’s telling you the exact environment the specimen sat in before the test ran – so you can judge whether that data applies to your application.
The Reference Conditions
A few terms show up repeatedly on data sheets:
- Room temperature: 20–30°C (68–85°F)
- Standard Laboratory Atmosphere: 23°C (73.4°F) at 50% ±5% relative humidity — the baseline most mechanical and electrical testing is referenced against
- Test temperature tolerance: ±2.0°C for test temperatures from -70°C to 180°C, with a wider allowance at higher temperatures up to 600°C
How to Read a Conditioning Code
The shorthand follows a consistent pattern:
hours / temperature (°C) / relative humidity (or immersion medium)
- A plus sign (+) between two of these strings means the specimen went through one conditioning step, then another, in sequence.
- “DES” means the specimen was desiccated (dried) over anhydrous calcium chloride.
A few worked examples:
| Code | What it means |
|---|---|
| 96/23/50 | Conditioned 96 hours at 23°C and 50% relative humidity |
| 48/50/water | Conditioned 48 hours at 50°C, immersed in water |
| 48/50 + 96/23/50 | Conditioned 48 hours at 50°C, then 96 hours at 23°C and 50% relative humidity |
| 48/50 + DES | Conditioned 48 hours at 50°C, then desiccated |
How to Read a Test Condition Code
Sometimes a data sheet adds a second part after a colon and a capital “T” — this describes the conditions the specimen was actually tested under (which can differ from how it was conditioned beforehand).
Prior conditioning : T – test temperature (°C) / test humidity (if controlled)
Examples:
| Code | What it means |
|---|---|
| 24/180: T-180 | Conditioned 24 hours at 180°C; tested at 180°C |
| 96/35/90: T-35-90 | Conditioned 96 hours at 35°C and 90% relative humidity; tested at 35°C and 90% relative humidity |
The Condition You’ll See Most Often: “Condition A”
Most data sheets you receive from us will reference Condition A, which simply means the specimen was tested as-received, with no special conditioning applied beforehand. This is the standard baseline specified under ASTM D709 and the applicable Mil-P specifications for laminated thermosetting materials, and it’s what most published mechanical and electrical property values are based on.
Why This Is Worth Knowing
If your application involves sustained heat, humidity, or moisture exposure, a Condition A data point may not tell the full story. Knowing how to read these codes lets you spot when a property was measured under conditions similar to yours — or ask us for data conditioned closer to your actual service environment.
Need additional information on material conditioning and quality control? Connect with Atlas Fibre representatives to learn more.