Pellon SF101 Shape-Flex vs Pellon Wonder-Under — Which Should You Use?

Pellon SF101 vs Pellon 805 Wonder-Under — Which Interfacing Should You Use?

Pellon makes many interfacing products — and the two we get the most questions about are SF101 Shape-Flex (a sew-in) and 805 Wonder-Under (a fusible web). They look similar on the roll but are completely different products. Here’s how to tell them apart and when to use each.

Linda’s Electric Quilters Expert Comparison
Pellon SF101 Shape-Flex Interfacing

Pellon SF101 Shape-Flex

SKU: Pellon SF101
From $7.99
Fusible woven interfacing • Adds body • Press-on • Cotton fabric feel • Great for bags & garments

Shop SF101
Pellon 805 Wonder-Under Fusible Web

Pellon 805 Wonder-Under

SKU: Pellon 805
From $6.99
Fusible web with paper • Bond two fabrics together • No sewing needed • Applique & crafts • Permanent bond

Shop Wonder-Under

Head-to-Head Comparison

Feature SF101 Shape-Flex 805 Wonder-Under
Product type Interfacing (woven) SF101 Fusible web/adhesive Wonder-Under
Purpose Add body and stability to fabric Bond two fabrics permanently together
Has paper backing No Yes — peel-and-fuse system Wonder-Under
Sewable after fusing Yes — designed to be sewn SF101 Yes, but stiffens needle area
Applique Not typical Yes — primary use case Wonder-Under
Bags & garments Excellent SF101 Not recommended
Reversible? No No — permanent bond
▶ Our VerdictSF101 adds body and structure to fabric — use it for bags, binding backings, and garments. Wonder-Under bonds two fabrics together — use it for applique, craft projects, and anywhere you want a fused (rather than sewn) join. Confusing one for the other wastes time and fabric.

Who Should Use Which?

Use SF101 Shape-Flex for…

  • Adding body to bag fabric
  • Stabilizing quilt binding strips
  • Garment construction and collars
  • Any project where fabric needs more structure
  • Anywhere you’ll still be sewing through it

Use Wonder-Under for…

  • Raw-edge applique on quilts
  • Fusing fabric shapes to backgrounds
  • Craft and home dec projects
  • Kids’ projects requiring no-sew joins
  • Securing binding before machine stitching

Frequently Asked Questions

Can I use Wonder-Under as interfacing?

No — Wonder-Under is a fusible adhesive web, not an interfacing. It will permanently bond your fabric to whatever it touches next and create a stiff, paper-like result. Use SF101 for interfacing needs.

Is SF101 the same as fusible batting?

No — SF101 is a woven fabric interfacing that adds body and stability. Fusible batting has a heat-activated adhesive on one or both sides to bond to the quilt top or back.

What is the difference between light, medium, and heavy interfacing?

Weight refers to how much body and stiffness the interfacing adds. Light (like SF101) is soft and drapey. Medium adds more structure. Heavy creates a very stiff result, used in bag bottoms and structured garments.

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