Welding Pad vs Welding Blanket vs Welding Curtain: How to Choose

Most people shopping for a welding blanket are really shopping for whichever hot work fabric happens to come up first, and the three products are not interchangeable. They carry three different duty ratings under one standard, FM 4950, and the difference between them is the difference between a fabric that stops molten slag and a fabric that burns through under it. This guide covers what each category is built for, which one can stand in for another, what the standard actually tests, and how to tell a real FM Approval from a catalog claim.

Last updated: August 3, 2026

The short version

Pad goes under the work and takes molten substances. Blanket goes nearby, horizontally, for sparks and heat from lighter work. Curtain does the nearby job vertically and keeps sparks from escaping the area.
Substitution runs one way only. A pad can serve as a blanket, and as a curtain if it stays flexible and dimensionally stable and does not melt or deform. A blanket can serve as a curtain on that same condition. Nothing works in the other direction.
Each category has its own pass criteria, which is why the labels matter. A pad has to show no ignition of the paper underneath at all. A blanket is allowed paper discoloration and limited burn holes. A curtain is not paper tested and instead has to resist melting and stay flexible.
FM 4950 sets no optical requirement. An approved welding curtain can be fully opaque, so it is not an arc glare screen. That is AWS F2.3M.
Tested to the standard and FM Approved are different claims. Only the second one means FM Approvals listed the product and audited the plant.

The three categories, and what each one is actually for

FM 4950 establishes three distinct categories with separate acceptance criteria, aimed at the applications most likely to be encountered. The names are not marketing labels. Each one describes a specific placement, a specific orientation, and a specific severity of exposure, and the test criteria follow from those assumptions.

Category	Where it goes	Orientation	Exposure it is built for	Combustible assumed underneath
Welding pad	Directly under the hot work	Horizontal	Severe. Molten substances, or heavy horizontal welding and cutting	Paper, ignition temperature 500°F (260°C)
Welding blanket	In the vicinity of the hot work	Horizontal	Light to moderate. Chipping, grinding, heat treating, sand blasting, light horizontal welding	Wood, with a limiting temperature of 500°F (260°C)
Welding curtain	In the vicinity of the hot work	Vertical	Light to moderate, same operations as a blanket	Not applicable. The job is keeping sparks inside the area

The assumed combustible in the last column is worth dwelling on, because it is where the engineering actually lives. A pad is evaluated on the premise that there is paper directly beneath it, which ignites around 500°F (260°C), and that molten substances are landing on top. So the pad has to resist burn-through and limit how much heat it transmits to its own underside. A blanket is evaluated on the premise that there is wood beneath it and sparks and heat above it, not molten metal. Same limiting temperature, much less severe exposure.

A curtain is doing a different job entirely. It is not protecting what is under it, it is preventing sparks and other sources of ignition from escaping a confined area. So on top of resisting melting, burning, burn-through and deformation, it has to stay flexible and dimensionally stable, because a curtain that shrinks or stiffens opens a gap and stops containing anything.

Which one substitutes for which

This is the single most useful thing in the standard and it is rarely stated plainly on a product page. The categories form a one-way ladder, because the pad faces the most severe test conditions and the strictest acceptance criteria.

A material that meets the performance criteria as a pad is considered qualified for use as a blanket. It also qualifies as a curtain, provided it maintains flexibility and dimensional stability and does not melt or deform.
Blankets and curtains see similar test conditions, with the blanket carrying the more critical acceptance criteria. So a blanket qualifies as a curtain on the same flexibility and stability proviso.
Nothing qualifies in the other direction. A curtain is not a blanket, and a blanket is not a pad, no matter how heavy the fabric feels in your hand.

The expensive mistake. Buying by weight or by price and putting a blanket where a pad belongs. Blankets are explicitly not expected to be subjected to molten substances, and a fabric never tested against molten metal contact can burn through and drop what it was supposed to catch onto whatever is underneath. If the job involves cutting, heavy welding or anything that produces molten substances, and there are combustibles below, the category you need is a pad.

What the standard actually tests

Knowing the test regime is what lets you read a spec sheet critically instead of taking a number on faith. Samples are conditioned at 73°F (23°C) and 50 percent relative humidity for at least 72 hours and tested within two hours of removal. Pads and blankets need a minimum of eight samples, four cut with the warp direction along the long dimension and four with the fill direction across it, since a woven fabric does not behave identically in both directions. Curtains need a minimum of two.

The acceptance criteria are not shared across the three categories. That is what makes the labels load-bearing rather than descriptive, and it is the detail most often flattened into a single claim on a product page. The criteria below are as stated in ANSI FM 4950-2024, sections 5.1 through 5.3.

Category	Fire and thermal resistance	Paper ignition
Welding pad	No burn-through. No individual thermocouple on the underside above 500°F (260°C). Charred areas must not crack.	No sign of ignition on any surface of the paper.
Welding blanket	The same three, except that areas exposed to molten metal or slag along the centerline of the burn pattern are excluded from the cracking requirement.	Discoloration is permitted. Burn holes are limited so a 1 in. (25 mm) diameter sphere cannot pass through without touching the edge of the burn.
Welding curtain	No melting, burning or burn-through. Hung vertically, it must stay flexible enough that at least 2 in. (51 mm) of slack lies flat on the floor at all times.	Not applied.

Charring embrittlement. Applied after the fire tests to pads and blankets. A fabric that survives the heat but turns brittle where it charred will not survive being folded and reused, which is how these products are actually handled.
Accelerated weathering. 1,000 hours of exposure per ASTM G154, after which a fresh specimen repeats the tests that apply to its category. This matters if the fabric lives outdoors or in daylight.

The rating is pass or fail against a category, not a temperature score. A fabric advertised only as good to some number of degrees has not told you which category it passed, which is the thing you actually need. And do not assume the weathering leg was run. Confirm it against the listing or the test documentation if the fabric will live outdoors.

Choosing for your operation

Work backwards from what the operation throws off and what is underneath or behind it, rather than from a product name.

Cutting, gouging, heavy welding over combustibles. Molten substances are in play, so this is pad territory, laid directly under the work.
Grinding, chipping, heat treating, sand blasting, light welding near equipment. A blanket, laid horizontally over what you are protecting.
Screening a bay, a walkway or an adjacent work area. A curtain, hung vertically, sized so sparks cannot travel around it. Remember that NFPA 51B works from a 35 ft radius, and that elevated or drafty work carries a larger area, so a curtain that only covers the obvious line of travel is undersized.
Bystanders need protection from arc glare. That is a separate specification. See the FAQ below and the NFPA 51B page, which covers the shielding requirement in the context of the 35 ft rule.

What "FM Approved" means, and what it does not

FM turns up here in two different forms, and they get conflated constantly, including by people selling the product. Keeping them apart is most of what you need to judge a supplier claim.

FM 4950 is a test standard, and there are two versions of it. FM Approvals publishes Class Number 4950, the Examination Standard for Welding Pads, Welding Blankets and Welding Curtains for Hot Work Operations, dated May 2024. That is the document an FM Approval is granted against. There is also an American National Standard version, ANSI FM 4950-2024, approved April 4, 2024, which is the one that turns up in reference lists. It was originally published in 2007 and reaffirmed in February 2013. Either way it says how to evaluate a fabric, and anyone can test to it. Note that neither document is designated "ANSI/FM" with a slash, common as that shorthand is in catalogs.
FM Approved is a listing decision. FM Approvals tests the product and audits the manufacturing plant and processes, with continuing surveillance. That is what a mark represents, and it attaches to specific style codes, not to a company.
FM Data Sheets are insurer guidance, not certification. Data Sheet 10-3 covers hot work management and calls for FM Approved pads, blankets and curtains among its recommendations. It is loss-prevention guidance rather than code, so how far it reaches you depends on your policy, your carrier and your own program. That is why a site can be fully code compliant and still be working through a carrier recommendation. Confirm what is actually required with your carrier.

How to check a claim. Ask for the style code, not the product family, and confirm that exact code and its category in the FM Approvals database. One mill will weave many fabrics, and two products from the same line can land in different categories. A datasheet that says a fabric was tested to FM 4950 is a manufacturer statement. A listing is a third-party one.

Other FM standards that touch industrial safety products

FM Approval standards are numbered by class. These are the ones that overlap the products covered elsewhere on this site.

Standard	Covers	Edition
FM 6050	Flammable and combustible liquid storage cabinets	December 2022
FM 6051-6052	Safety cans and filling, supply and disposal containers	September 2025
FM 6061	Flame arresters, including those fitted to safety cans	See FM Approvals

Sizing hot work fabrics for a shop or a shutdown?

Tell us what the work throws off and what you are protecting, and we will quote the right category rather than the cheapest fabric. Custom sizes are normal in this category. We do not make code determinations or certify your setup.

or call 714-248-6555 · email partners@usmadesupply.com

What to check before you buy

The category, for the exact style code. Not the product family, and not the heaviest item in the catalog.
Size, and whether it is seamless. Products meeting the criteria are not limited in length or width provided they are of seamless construction, and perimeter seams are allowed. A product that joins pieces together needs its seam assessed, and retested if the seam differs from the field of the material. So a large custom size is a reasonable ask, and a pieced assembly is a reasonable question.
Whether it went through accelerated weathering. Relevant for anything living outdoors or in daylight. Confirm it against the listing or the test documentation.
Grommets and how you will actually hang or anchor it. Fabric articles generally ship as the sewn article with grommets. Frames, poles and stands are usually a separate purchase from a different supplier, which is worth knowing before you plan a free-standing screen.
Whether your carrier requires an approval. If the property insurance follows FM, "tested to the standard" may not satisfy a recommendation that names FM Approved products.

One more practical note. These fabrics are consumables with a service life, not fixed equipment. The charring embrittlement test exists precisely because a fabric gets folded, stored and reused. A pad that has taken repeated molten metal contact and shows cracking where it charred is finished, whatever it cost.

Frequently Asked Questions

What is the difference between a welding pad, a welding blanket and a welding curtain?

Placement, orientation and severity. A welding pad goes directly under the work, lies horizontally, and is built to take molten substances without burning through or letting the underside get hot enough to ignite paper. A welding blanket goes in the vicinity, also horizontally, and handles sparks, flames and heat from lighter operations such as grinding and chipping, but is not expected to take molten metal. A welding curtain does the same duty vertically, and its job is to stop sparks escaping the area. FM 4950 defines all three and gives each its own acceptance criteria.

Can I use a welding blanket as a welding pad?

No. Substitution only runs one way, toward the lighter duty. Under FM 4950 the pad faces the most severe test conditions and the strictest acceptance criteria, so a material qualified as a pad is considered qualified as a blanket, and qualified as a curtain provided it stays flexible and dimensionally stable and does not melt or deform. A blanket may serve as a curtain on the same proviso. Nothing qualifies downward into a more severe category. Putting a blanket under molten metal is the substitution that actually starts fires.

Does "tested to FM 4950" mean a product is FM Approved?

Not by itself. FM 4950 is the test standard. FM Approved is a listing decision made by FM Approvals, which involves testing the product and auditing the plant and processes that make it, with ongoing surveillance. A manufacturer can accurately say a fabric was tested to the standard without that fabric being a listed, FM Approved product. If the approval matters to you, and it will if your property carrier follows FM, verify the specific style code in the FM Approvals database rather than relying on a catalog claim.

Do welding curtains protect against arc glare?

Not necessarily, and this is the most common mistaken assumption about them. FM 4950 evaluates a curtain as a spark barrier. It sets no optical requirement, so a curtain that fully satisfies the standard may be completely opaque and offers no defined protection to bystanders from arc glare. Screening people from the arc is a separate specification, AWS F2.3M, which covers transparent welding curtains and screens. If you need both functions, confirm both, because one does not imply the other.

What temperature does a welding pad have to hold?

For a pad the criteria are that there is no burn-through, that no individual thermocouple placed on the underside exceeds 500°F (260°C), and that any charred areas do not crack when subjected to the charring embrittlement test. There is also a paper ignition test, in which there must be no sign of ignition on any surface of the paper placed underneath. The 500°F figure comes from the ignition temperature assumed for paper under a pad, and the same limiting temperature is used for blankets as representative of the endothermic phase of wood degrading thermally.

Is there a size limit on an FM 4950 rated pad or blanket?

Not on length or width, provided the article is of seamless construction. Seams along the outer perimeter are allowed. Where a product joins two or more pieces of material together, the seam has to be assessed, and if its construction differs from the field of the material then additional testing is required with the seam positioned at the most critical location and orientation. In practice that means a large custom size is a normal thing to quote, but a seamed assembly is a question to ask about rather than assume.