Since this is only backing, no it isn't a floating line. It's not coated and will sink unlike the main fly line, assuming that it is a floater.

SF Fly Fishing Backing Line Braided Trout Line

SF Fly Fishing Backing Line Braided Trout Line

Q: I have 5wt line. Which backing should i get? (20lb or 30lb)?

it depends on your fly reel. all fly reels are not equal. I have a 7/8 wght fly reel and end up only using maybe not even half of the 30lbs backing that I got. if you are not catching 30lb plus fish, go with 20lb backing. but if your reel is holds a lot of line than go with 30lb. hope this helps☺have a great day. this line is soft/strong & it benefits the fly line well.

Q: what are the diameters (in mm) for each one?

The line it’s self has all the info I received. Sorry I do not have a caliber gauge to measure mm.

Q: Can I use on my fishing rod for blue gills?

This product is FLY LINE BACKING... This product is intended to be used as backing line on a fly reel, NOT as a main line. If you're using your set up to fish for blue gills (or anything else really), yeah, this will work on your fly reel, followed by fly line, then a leader, and finally some tippet to the fly itself.

Product ID: 202828010

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Details

Material
Polyester
Color
Blue-100M
Fishing Line Type
Braided
Brand
SF
Line Weight
20 pounds

🎣20lb & 30lb breaking strength

🧵8-strand hollow braid

🛡️UV & rot resistant polyester

Frequently Bought Together

Description

🎣 Elevate your fly fishing game with backing line that’s built to perform and last.

UV ROT PROOF - Crafted from premium polyester to withstand sun and water exposure season after season.
SLIM YET STRONG - Max reel capacity without bulk—braided for unbeatable abrasion resistance.
TRUSTED BY PROS - Engineered backing line that complements all fly lines—because your gear deserves the best.
EFFORTLESS CASTING - Low friction design protects your rod guides and ensures smooth, tangle-free casts.
VERSATILE STRENGTH OPTIONS - Choose 20lb for freshwater finesse or 30lb for tackling salmon, saltwater, and pike.

The SF Fly Fishing Backing Line is a high-quality, 8-strand hollow braided polyester line offering superior abrasion resistance, UV and rot protection, and low friction for smooth casting. Available in 20lb and 30lb strengths, it’s designed to maximize reel capacity and durability, making it ideal for both freshwater and saltwater fly fishing.

Specifications

Material	Polyester
Color	Blue-100M
Fishing Line Type	Braided
Brand	SF
Line Weight	20 pounds
Breaking Strength	20 Pounds
Strand Type	Multi
Manufacturer	SF
Item Package Dimensions L x W x H	4.53 x 3.54 x 1.02 inches
Package Weight	0.05 Kilograms
Item Dimensions LxWxH	3.94 x 3.94 x 0.79 inches
Brand Name	SF
Suggested Users	mens
Part Number	FL0409B
Size	20LB 100m/108yds
Sport Type	Fishing
Skill Level	All
Fishing Technique	Fly Fishing

Have a Question? See What Others Asked

I have 5wt line. Which backing should i get? (20lb or 30lb)?

what are the diameters (in mm) for each one?

Is it floating line

Can I use on my fishing rod for blue gills?

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