SA Amplitude MPX Review: The Half Size Heavy Line
Buy it if your rod is fast or medium-fast and feels dead at short range, because this line is built half a size heavy specifically to fix that. Skip it if you fish a slow or moderate blank at distance, or if you fish hot southern water, because Scientific Anglers rates this coating for moderate and cold climates.
Built half a size heavy on purpose, and why that is a feature on some rods and a fault on others.
Scientific Anglers Amplitude Smooth MPX Taper, WF-5-F
Under $250
Scientific Anglers' general presentation trout line in a 5 weight, built half a size heavy with the AST Plus slickness additive.
Check price on AmazonSpecifications
| Configuration | WF-5-F, MPX taper, optic green |
|---|---|
| Weighting | Made a half size heavy, which Scientific Anglers states is to load fast action rods |
| Additive | AST Plus slickness additive, for shooting ability and durability |
| Intended species | Trout, panfish, bass, grayling and carp, and also useful for steelhead, salmon and pike |
| Best with | Large dry flies, nymphs and streamers |
| Climate rating | For use in moderate and cold climates |
| Budget | Under $250 |
Specifications above come from Scientific Anglers' published description of the Amplitude Smooth MPX. Treat pricing as approximate, since Amazon pricing moves.
What it does well
- Scientific Anglers tells you plainly that it is half a size heavy. That is honest, useful information most manufacturers leave you to discover by feel.
- Half a size heavy is exactly what a fast rod needs to load at the 25 to 35 foot range where most trout are caught.
- AST Plus is a slickness additive rather than a coating gimmick, and shooting distance is the property owners notice first.
- It is a genuine all round taper: Scientific Anglers lists it for large dries, nymphs and streamers rather than one narrow use.
Where it falls short
- On a slow or moderate rod at distance, the extra mass can feel like too much. This line is a solution to a specific problem, and if you do not have that problem it is a mismatch.
- Scientific Anglers rates it for moderate and cold climates. Fly line coatings soften in heat, and using a cold climate line on hot southern water is a documented way to get a line that feels tacky and shoots poorly.
- under $250 for a line, which is more than some complete beginner outfits cost in total.
- Scientific Anglers does not publish head length or grain weight for this line in the Amazon listing, so we are not going to state either. Those figures live on Scientific Anglers' own product page.
What owners report
Published owner reviews of the Amplitude Smooth range are consistent that the lines shoot exceptionally well and that the smooth version is quieter through the guides than the textured versions, which is the main reason people choose it. Reviewers pairing it with fast rods are the most positive group, which is exactly what Scientific Anglers' own description predicts.
The recurring criticism is price, followed by a smaller theme about the half size heavy design feeling like too much on softer rods. Both are predictable from the specification rather than surprises, which is a reasonable sign that the manufacturer's description of this line is accurate.
How it fits with the rest of your kit
Everything about this line depends on the rod you hang it on, so start with the line weight calculator to confirm the class, and then read the weight forward against double taper comparison to understand why front loaded mass is the modern default and what it costs in delicacy at range.
On the rod side, this line is the natural partner for a fast blank like the Redington Vice, and a less natural one for a soft short rod like the Redington Classic Trout. The trout fly line roundup covers the cheaper field, and the RIO Elite Gold is the long head rival built on the opposite philosophy.
Who it suits
- Owners of fast and medium-fast rods that feel lifeless with a true to standard line.
- Anglers who fish a mix of big dries, nymph rigs and small streamers with one line.
- People fishing moderate and cold climate water, which is what Scientific Anglers rates this coating for.
Who should skip it
- Owners of slow or fibreglass rods, who will find the extra mass unhelpful.
- Anglers on hot southern tailwaters in summer, who should choose a line rated for warm climates.
- Delicate presentation specialists on flat water, where a lighter, longer front taper lands more softly.
Alternatives worth considering
RIO Elite Gold Fly Line, WF5F, 90 feet
Under $250
RIO's flagship all round line at under $250, built with a long head and back taper for stability at distance rather than mass up front. The better choice on open water and longer casts.
Check price on AmazonScientific Anglers Magnitude Smooth Trout Expert, 10 foot clear tip, WF5F
Under $250
under $250 for a Scientific Anglers line with a 10 foot clear tip, which genuinely helps on flat clear water and stillwater where line colour lands inside a trout's window.
Check price on AmazonSF Weight Forward Floating Fly Line, WF5F, 90 feet
Under $25
under $25 for a weight forward floating 5 weight line, which is the sensible starting point for a first season. Upgrade once you know what your rod wants rather than before.
Check price on AmazonKeep reading
- Weight forward against double taper fly line
- Line weight calculator
- Best fly line for trout
- RIO Elite Gold review
- Redington Vice review
This review draws on published specifications, manufacturer figures and the consensus of verified owner reviews. We have not tested this product ourselves, and we say so rather than implying otherwise. As an Amazon Associate we earn from qualifying purchases.
Frequently asked questions
What does half a size heavy mean on a fly line?
It means the line carries more mass in its first 30 feet than the nominal line class calls for. A 5 weight line is standardised at 140 grains in that length, and a half size heavy 5 weight sits between a true 5 and a true 6. Manufacturers do this deliberately so fast rods load at short range, and Scientific Anglers says so openly for the MPX.
Will the MPX overload my rod?
Not in any damaging sense. Line class ratings are about loading feel, not structural limits, and half a size heavy is a small step. What it can do is make a slow or moderate rod feel sluggish at distance, because the blank is already loading fully with less line out. On a fast rod it does the opposite and makes short casts come alive.
Scientific Anglers MPX versus RIO Elite Gold, which is better?
Neither, and they solve different problems. The MPX puts extra mass up front to load fast rods close in. The Elite Gold uses a long head and back taper for loop stability at distance. Match the line to the rod and the range you fish: fast rod and short water points to the MPX, open water and longer casts points to the Elite Gold.
Does climate rating on a fly line matter?
Yes, more than most people expect. Fly line coatings are formulated to stay supple across a temperature band, and Scientific Anglers rates this line for moderate and cold climates. A cold climate line on hot water goes tacky and shoots poorly, and a tropical line in cold water goes stiff and coils. If you fish hot southern water in summer, buy a line rated for it.
Is a $100 fly line a worthwhile upgrade from an entry line?
The jump from a $15 line to a good line is the biggest single improvement most people can buy, and it is bigger than the jump from a $200 rod to a $500 one. The jump from a $60 line to a $100 one is much smaller. If you are still on a beginner line, upgrade. If you already fish a decent line, spend the money on time on the water instead.
How we choose: we compare published manufacturer specifications, line and leader standards, and verified owner reviews across retailers. We do not test gear in person, and every diameter, grain weight and breaking strength quoted here is the manufacturer's published figure unless we say otherwise, so check the spool label before you trust a number. Nothing here is professional instruction. Wading moving water is the real hazard in this sport: wear a snug wading belt, know the water temperature, and turn back rather than push through a crossing you are unsure of.
