Scientific Anglers Amplitude Smooth Infinity
In Stock • Bozeman, MT
- Features the revolutionary AST Plus slickness additive for superior shooting ability and increased durability
- Extremely versatile general-purpose taper designed for most freshwater species; an excellent fly line for trout, grayling, panfish, bass, carp, steelhead, salmon, and pike
- Made a half-size heavy to load fast-action rods, but works well with a variety of rod actions
- Extended head length for long-distance casts and superior mending ability
- Excellent for dry flies, nymphs, and streamers
Description
The conventional wisdom in fly fishing is that there’s no such thing as a do-it-all freshwater line. The SA Amplitude Infinity makes a case against that view. Built on an extended head (47’ at 3 wt through 52’ at 8 wt) with a substantial 7-foot front taper and a complex three-section rear taper, the Infinity handles dry flies, nymphs, streamers, and indicator rigs on the same reel without requiring a line change. It does this because the taper is deliberately designed to sit between extremes — not as aggressive as a shooting head, not as delicate as a specialist presentation line — positioned to handle the full range of techniques most anglers encounter in a day of freshwater fishing.
The half-size-heavy construction puts extra mass in the head for loading fast-action rods at close range and turning over heavier flies without a dedicated line change. The long head mends cleanly on broad, slow currents and carries line in the air for the longer presentations required on tailwaters and spring creeks. AST Plus integrated into the coating maintains shooting performance across seasons without re-application. The Camo color pattern on the belly section reduces the line’s visible profile to fish in clear conditions.
Available in Smooth and Textured versions. The Textured version adds Floating Texture to the tip section for enhanced dry fly flotation, and Shooting Texture to the running line for reduced guide friction. 90-foot total length. Cold and moderate climates only — not suitable for tropical or high-heat use.
Features
• Extended Variable Head (47–52’) — Head length increases with line weight. Longer than most standard freshwater WF lines; allows carrying line at distance, mending on broad currents, and presenting across a wide range of cast distances.
• ½ Size Heavy — Extra mass in the head loads fast-action rods at close range and helps turn over heavier flies and indicator rigs.
• Substantial 7-Foot Front Taper — Balanced between delivery power (for streamers and heavier patterns) and delicacy (for smaller dry flies). Not specialized for either extreme; designed to handle both.
• Complex Three-Section Rear Taper — Progressively acute sections toward the running line contribute to the line’s mending ability and carrying performance at longer distances.
• AST Plus Slickness Additive — Integrated into the coating for sustained shooting performance across the full life of the line.
• Camo Color Technology — Multi-tone color pattern on the belly section reduces the line’s visible profile to fish in clear water.
• Smooth Version: Improved Dry Tip — SA’s tip coating technology for enhanced flotation on the tip section.
• Textured Version: Floating Texture Tip — Microreplication pattern increases surface contact with water for maximum dry fly flotation; keeps the tip riding higher in the film.
• Braided Multifilament Core — Provides suppleness and strength throughout the temperature range of cold and moderate freshwater environments.
• Cold & Moderate Climates Only — Not suitable for tropical or high-heat use.
• 100% Made in USA.
Rod Pairing
| Rod Action | Pairing | Notes |
|---|---|---|
| Fast Action | Ideal | The ½ overweight and extended head load fast-action rods quickly at close range while allowing more line to be carried for distance presentations and roll casts. |
| Medium-Fast Action | Works Well | Performs well on medium-fast rods. The long rear taper and substantial front taper provide consistent timing and smooth energy transfer across a wide range of casting distances. |
| Medium Action | Use with Care | The long head and ½ overweight design can overload softer medium-action rods when carrying more line. It works well at shorter distances, but stepping down a line weight or choosing a more moderate taper is often a better option for slower rods. |
Size Guide
| Line Weight | Head Length | Head Weight | Grain Wt. (30') | Species / Technique |
|---|---|---|---|---|
| WF-3-F | 47.0' / 14.3M | 155GR / 10.0G | 110GR / 7.2G | Small stream trout, grayling, panfish; light dry flies and small nymphs |
| WF-4-F | 48.0' / 14.6M | 190GR / 12.3G | 130GR / 8.5G | Trout, grayling, panfish; standard dry flies, nymphs, and small streamers |
| WF-5-F | 49.0' / 14.9M | 225GR / 14.6G | 150GR / 9.8G | Trout, grayling, bass; the most versatile all-around freshwater weight for dry flies, nymphs, streamers, and indicator rigs |
| WF-6-F | 50.0' / 15.2M | 265GR / 17.2G | 175GR / 11.2G | Trout, bass, carp, steelhead nymphing; heavier streamers, larger dry flies, and indicator rigs |
| WF-7-F | 51.0' / 15.5M | 305GR / 19.8G | 200GR / 12.8G | Steelhead, salmon, bass, carp; big streamers, heavy indicator rigs, and larger rivers |
| WF-8-F | 52.0' / 15.8M | 350GR / 22.7G | 225GR / 14.5G | Steelhead, salmon, pike, large bass; heavy streamers, large surface flies, and single-hand spey presentations |
FAQ
What are the parts of a fly line and what does each section do?
A weight-forward fly line has five sections: Running Line: The thin, level back section that shoots through guides on the forward cast. The Infinity’s smooth Shooting Texture running line (Textured version) reduces contact with guide surfaces for improved shooting distance. Rear Taper: The transition from running line to belly. The Infinity is specifically noted for its complex rear taper — three progressively more acute taper sections that decrease in diameter toward the running line. This multi-section rear taper is part of what gives the Infinity its mending ability at longer distances. Belly: The thickest, heaviest section and primary weight carrier. The Infinity’s head length increases with line weight (47’ at 3 wt through 52’ at 8 wt) — longer than most standard freshwater weight-forward lines. This extended belly allows carrying more line in the air for distance presentations and provides more surface area for mending. Front Taper: The transition from belly to tip. The Infinity has a substantial 7-foot front taper that provides enough stiffness to turn over streamers and larger flies while retaining the delicacy to present smaller patterns without collapsing. Tip: The final section where the leader connects. The Smooth version features SA’s Improved Dry Tip for enhanced flotation; the Textured version uses Floating Texture microreplication on the tip section to maximize surface contact with the water and keep dry flies riding higher.
How does the Infinity taper work across such a wide range of techniques?
The Infinity’s versatility comes from three design choices working together. First, the half-size-heavy construction puts more mass in the head than a standard-weight line, which helps fast-action rods load at short range and turns over heavier flies without a specialized streamer line. Second, the substantial 7-foot front taper provides a balance between delivery power (needed for streamers and larger patterns) and delicacy (needed for smaller dry flies). It is not as aggressive as a dedicated streamer taper, but not as fine as a dedicated dry fly taper — deliberately designed to handle both. Third, the extended head length (47–52’ depending on weight) and complex three-section rear taper allow the line to be carried in the air at longer distances, mended on broad, slow currents, and roll-cast cleanly — all critical in the spring creek and tailwater situations the Infinity is frequently used for.
What is the difference between the Smooth and Textured versions?
Both versions share the same taper, grain weights, head lengths, and AST Plus formulation. The differences are in the tip and running line surface treatments: Smooth (Amplitude Smooth Infinity): Improved Dry Tip on the tip section (SA’s smooth coating technology for enhanced flotation). Standard smooth AST Plus coating on the running line. Textured (Amplitude Textured Infinity): Floating Texture on the tip section — a microreplication pattern that increases the line’s surface contact area with the water, providing enhanced buoyancy and keeping dry flies riding higher than the Smooth version. Shooting Texture on the running line for reduced guide friction and extended shooting distance. For anglers who fish dry flies regularly, the Textured version’s Floating Texture tip provides a meaningful practical advantage by keeping the tip riding in the film rather than dipping below it, which helps with line mending and prevents drag on the fly. For anglers who primarily nymph or throw streamers, the Shooting Texture running line’s distance advantage is more relevant.
What is AST Plus and what does it do for a freshwater line?
AST Plus (Advanced Shooting Technology Plus) is SA’s slickness additive integrated into the line coating rather than applied as a surface treatment. Because it is part of the coating, it continuously migrates to the outer surface as the outer layer wears, maintaining shooting performance over the full life of the line rather than degrading after one or two seasons. For a freshwater line that will be used across multiple seasons in varying conditions, the sustained slickness of AST Plus provides measurable long-term value compared to lines treated with surface dressings that wear off.
What is the Camo technology?
The Amplitude Smooth Infinity uses SA’s Camo color technology on the belly section of the line — a multi-tone color pattern that blends more naturally with water and sky backgrounds than a solid-color line. The idea is that a camouflaged line belly is less visible to fish looking up toward the surface. It is most relevant in clear, shallow water where fish can see the line overhead. The Camo pattern is visible to the angler for tracking purposes but produces a less distinct outline to fish than a solid bright color.
Product Video
