Fly Tying Thread & Denier Reference Guide
Fly tying thread controls how a fly is built, how durable it is, and how clean it looks. Thread diameter, strength, material, and color all affect the tying process. This guide explains common fly tying thread types, denier sizing, and how to choose the right thread for different patterns.
Quick links:
- Thread materials
- Denier and sizing explained
- Choosing thread by fly type
- Thread for beginner fly tiers
- Common thread mistakes
Thread materials
Nylon thread
Nylon thread is the most commonly used fly tying thread. It offers good strength, smooth wraps, and easy handling. Nylon is versatile and works well for most dry flies, nymphs, and streamers.
Polyester thread
Polyester thread is strong and abrasion resistant. It is often chosen for durability in streamers and larger flies.
Gel-spun polyethylene (GSP)
GSP thread is extremely strong for its diameter. It is commonly used for spinning deer hair and tying large or heavy-duty patterns. Care should be taken due to its cutting strength.
Denier and sizing explained
Denier measures thread thickness. Higher denier numbers indicate thicker thread.
| Denier | Common uses |
|---|---|
| 30–50 | Small dry flies, midges |
| 70 | Standard dry flies and small nymphs |
| 140 | Nymphs, streamers, general tying |
| 210+ | Large streamers, bass flies, deer hair |
Different manufacturers label thread differently, so comparing within the same brand is often most consistent.
Choosing thread by fly type
- Dry flies: 30–70 denier for clean profiles
- Nymphs: 70–140 denier depending on size
- Streamers: 140–210 denier or GSP for durability
- Deer hair flies: GSP or heavier denier thread
Thread for beginner fly tiers
Beginners can cover most tying needs with:
- 70 denier thread in black, brown, and olive
- 140 denier thread for larger flies
Common thread mistakes
- Using thread that is too heavy for small flies
- Breaking fine thread with excessive tension
- Ignoring color when building segmented bodies