A-A-55220 is a U.S. government Commercial Item Description covering intermediate modulus para-aramid filament sewing thread used in aerospace, military, and safety-critical applications. The specification defines key performance requirements such as tensile strength, linear density, and yield per pound, but does not control construction variables like twist (TPI), finish chemistry, or processing—meaning real-world performance can vary significantly between compliant products.
Para-aramid sewing threads are widely used in aerospace, military, and safety-critical textile assemblies where exceptional strength, heat resistance, and durability are required. One of the most important government specifications governing these materials is A-A-55220, which defines performance requirements for intermediate modulus para-aramid filament sewing threads.
Unlike spun aramid sewing threads, A-A-55220 threads are manufactured from continuous filament para-aramid yarns, delivering higher tensile strength, lower lint generation, improved abrasion resistance, and more consistent seam performance in structural applications.
What Is A-A-55220?
A-A-55220 is a Commercial Item Description (CID) that defines the performance requirements for intermediate modulus para-aramid sewing thread used in both machine and hand sewing applications. The specification covers thread intended for use in clothing, equipage, aerospace systems, and safety equipment.
The document replaced the earlier military specification MIL-T-87128, transitioning from a construction-based standard to a performance-based specification. While MIL-T-87128 defined construction parameters such as twist levels and thread build, A-A-55220 focuses on measurable outputs like tensile strength and yield—allowing manufacturers flexibility in how the thread is engineered.
This shift is significant, as two threads can both meet A-A-55220 requirements while exhibiting very different handling, abrasion resistance, and sewing performance depending on their construction.
Under A-A-55220, the thread may be furnished as:
- Twisted Soft Multiple Cord (Bonded & Unbonded)
- Monocord (Flat Filament Construction)
Threads are typically finished or lubricated to support high-speed sewing, reduce friction, and improve handling characteristics during processing.
Why Filament Threads Instead Of Spun Threads?
The primary difference between A-A-55195 Mil Spec For Spun Kevlar® Sewing Thread and A-A-55220 is the yarn construction. Spun thread is made from short staple fibers twisted together, while filament thread uses continuous para-aramid filaments.
Spun aramid thread is produced from short staple fibers and is commonly used in protective clothing, firefighting gear, and industrial PPE.
This construction provides a softer hand, improved flexibility, and better dyeability, making it well-suited for apparel applications.
However, the presence of short fibers leads to increased lint, reduced abrasion resistance, and lower structural integrity compared to filament constructions.
Filament para-aramid threads use continuous filaments, resulting in significantly improved mechanical performance.
These threads provide higher tensile strength, superior abrasion resistance, minimal lint generation, and more consistent sewing behavior under load.
As a result, filament threads are preferred in engineered textile systems where seam strength and long-term durability are critical.
Typical applications for filament para-aramid thread include:
- Parachutes And Air Delivery Systems
- Safety Harnesses
- Military Equipment
- Aerospace Sewn Assemblies
- Load-Bearing Textile Components
A-A-55220 Thread Types And Performance Tables
The specification defines requirements for para-aramid filament thread constructions based on performance outputs such as linear density, yield, and minimum breaking strength.
Important: The specification does not define construction variables such as twist level (TPI), twist direction, or finish chemistry. These factors are left to the manufacturer and can significantly impact real-world performance.
Table – Twisted Soft Multiple Cord
| TEX | Denier | Ply | Yd/lb | Break Strength (lbs) |
|---|---|---|---|---|
| 40 | 400 | 2 | 10,000 | 14 |
| 60 | 600 | 3 | 6,700 | 23 |
| 80 | 800 | 4 | 5,000 | 30 |
| 120 | 1200 | 3 | 3,350 | 45 |
| 210 | 2000 | 5 | 2,100 | 64 |
| 400 | 4000 | 4 | 1,050 | 135 |
| 450 | 4500 | 3 | 900 | 150 |
| 800 | 7500 | 5 | 550 | 225 |
Table – Monocord (Flat Filament Construction)
Monocord thread is produced using a single bundle of parallel continuous filaments with minimal or no twist. This creates a flatter, ribbon-like profile compared to twisted multi-ply constructions.
- Minimal Twist
- Flat, Ribbon-Like Profile
- Higher Fiber Efficiency
- Different Handling And Abrasion Behavior
| TEX | Denier | Type | Yd/lb | Break Strength (lbs) |
|---|---|---|---|---|
| 21 | 200 | Monocord | 21,500 | 7.5 |
| 40 | 400 | Monocord | 10,750 | 15 |
| 105 | 1000 | Monocord | 4,300 | 45 |
| 150 | 1500 | Monocord | 2,875 | 70 |
| 240 | 2250 | Monocord | 2,175 | 95 |
| 300 | 3000 | Monocord | 1,450 | 130 |
Important: As with twisted constructions, A-A-55220 defines minimum performance values but does not control processing variables such as filament alignment, tension, or finishing. These factors can significantly influence sewing performance and durability.
Common Para-Aramid Fiber Types Used For Filament Thread
Commercial filament para-aramid thread is typically manufactured using high-performance fibers such as:
These fibers provide high tensile strength, thermal stability, and durability required for aerospace and safety-critical applications.
Rocket-Fibers High Performance Materials
Rocket-Fibers supplies high-performance fibers used in advanced textile, aerospace, and composite applications where durability and structural strength are required.
