Guides & Education
How to Choose EMF Shielding Fabric: GSM, Width and dB Explained for Buyers
What GSM, roll width and dB ratings actually control in EMF shielding fabric — yield math, a five-step checklist, and the questions to ask suppliers.
A shielding fabric spec sheet throws three numbers at you at once: GSM, width and dB. Each controls a different part of the outcome — one drives feel and yield, one drives cost, one drives the claim you can support. Read them in isolation and you will overpay or underspecify. Here is what each number actually tells you, and a checklist that ties them together.
What GSM Actually Tells You
GSM means grams per square meter — fabric weight. It shapes drape, hand feel, durability and, indirectly, your yield per linear meter. What it does not do is measure shielding: there is no reliable conversion from GSM to dB, because attenuation comes from the conductive structure and how it is engineered, not from weight alone. Treat any supplier who quotes dB "per GSM" with caution.
Use GSM to shortlist for the product, not to predict performance. For cut-and-sew apparel, mid-weight constructions are the workhorse zone — Zimo's SILVER 75#B, for example, is a 175 GSM blend of 42% silver fiber, 53% cotton and 5% polyester, and it handles like a quality mid-weight cotton. Heavier, denser constructions suit panels and curtains, where drape matters less.
How Width Drives Your Landed Cost
Quotes usually state a nominal roll width, but the number that matters is usable width — what you can actually cut after selvedges and edge exclusions. All yield math runs on usable width, so get it in writing.
The arithmetic is simple: linear meters required = total area needed ÷ usable width. Say a curtain panel measures 1.4 m wide by 2.4 m high — about 3.4 m². On a fabric with 1.5 m of usable width, each panel consumes 2.4 linear meters with no seaming. If usable width drops to 1.2 m, the same panel no longer fits in one pass: you either seam two pieces (labor plus a visible join) or waste width on every cut. Multiplied across a production run, that difference quietly becomes one of the largest cost levers in the BOM.
Wider is not automatically better — very wide rolls may need different cutting tables — but narrower-than-expected usable width is the classic surprise in fabric sourcing. Always cost from usable width, not nominal.
Reading dB Numbers the Right Way
Decibels are logarithmic: every additional 10 dB means the transmitted signal drops to about one-tenth of the power. That is why the gap between a 20–40 dB fabric and a 60–90 dB fabric is not "a bit better" — it is a different order of shielding.
Zimo publishes manufacturer-tested bands rather than single hero numbers, because attenuation varies with frequency and construction:
Copper-nickel fabric: 60–90 dB (manufacturer-tested)
Silver fiber, dense construction: 50–80 dB (manufacturer-tested)
Silver fiber, open mesh: 20–40 dB (manufacturer-tested)
Stainless steel fabric: no dB rating published
Two habits make these numbers usable. First, always ask which construction and which frequency range a quoted dB figure refers to — a number without that context cannot be compared. Second, carry the "manufacturer-tested" qualifier through to your own product claims, and verify against your intended use before you print it.
Three Worked Scenarios
Maternity apparel line. Comfort decides repeat purchases, so dense silver fiber around the 175 GSM class is the natural shortlist; the 50–80 dB manufacturer-tested band supports consumer claims without a stiff hand. Choose width for marker efficiency, since apparel cuts many small panels.
Curtain or canopy range. Panels are wide and seams are visible, so pick copper-nickel for the 60–90 dB manufacturer-tested band, then select a usable width that covers standard panel sizes with minimal seaming.
Accessory capsule. Scarves and liners live or die on feel and weight. Silver mesh at 20–40 dB (manufacturer-tested) keeps pieces light and breathable while still delivering a measurable, documentable spec.
A Five-Step Selection Checklist
Define the product and its care expectations — a weekly-washed garment and a rarely-washed curtain fail differently.
Set an attenuation band with its qualifier (manufacturer-tested) and the frequencies you care about.
Pick a GSM class for drape, hand and durability — not for a dB promise.
Compute yield from usable width and compare suppliers on cost per finished product.
Validate with swatches and one wash trial before committing to production.
FAQ
Does higher GSM mean better shielding?
No. GSM describes weight; shielding comes from the conductive structure. Two fabrics at the same GSM can sit in different dB bands, and one family can come in several GSM values.
What usable width should I assume for costing?
None — ask the supplier. Nominal width can lose several centimeters to selvedge, and assuming nominal width is how runs end up short. Get usable width in writing and run all yield math on it.
Why do dB figures come as ranges?
Because attenuation changes with frequency and with construction details. An honest range — like Zimo's 60–90 dB manufacturer-tested band for copper-nickel — tells you more than a single flattering number.
Is 20–40 dB enough for a consumer accessory?
For many accessories, yes — mesh keeps the piece wearable, and the band is manufacturer-tested and documentable. Whether it fits your claim is a product decision; verify with your own measurement before you market it.
How do I compare two suppliers fairly?
Same method, same frequency points, same basis: usable width, GSM class and dB qualifier. If one quote omits any of these, the omission is itself information.
Get a Spec Sheet You Can Cost Against
Zimo manufactures silver fiber, copper-nickel and stainless steel shielding fabrics with no minimum order quantity and customization available. Send your product concept and target spec via zimo-cn.com/contact-us and we will return a datasheet with GSM, usable width and manufacturer-tested dB figures — the three numbers this article taught you to read.
Request a datasheet and swatches via our contact page.
Related Reading
Silver Fiber vs Copper Nickel Fabric: Which One for Your Product Line?
How EMF Shielding Fabric Is Tested: Methods, Standards and What the Numbers Mean
How to Wash EMF Shielding Fabric: Care Instructions That Preserve Performance
MOQ Explained: Why Fabric Suppliers Set Minimum Orders and How to Work With Them
