Labels and spec sheets

What the numbers and marks on a window covering's label or spec sheet mean: openness factor, visible transmittance and solar reflectance, the AERC energy label, the Best for Kids label, the cord warning, fiber content, UV percentages on film, and anchor ratings.

Each section below takes one number or mark you will meet on a label, a spec sheet or a product page, says what it measures, and says what it does not tell you. Read the section when you meet the number; there is no order.

On this page:

• Openness, visible transmittance and solar reflectance
• The AERC energy label
• The Best for Kids label
• The cord warning label
• Fiber content and care
• Ultraviolet percentages on film and fabric
• Anchor, rod and track ratings
• NFPA 701 on a fabric sheet

Openness, visible transmittance and solar reflectance

These three figures appear on spec sheets for solar shades and screen fabrics. Lutron's selection guide defines them (Commercial Roller Shade Selection Guide):

• Openness factor (OF): the percentage of direct light that passes straight through the gaps in the weave, set mainly by how tight the weave is. Draper gives the typical range as 1 to about 13 percent (What Affects View-Through?, 2022). A swatch card may call the figure approximate.
• Visible transmittance (Tv, or VLT on film): the percentage of visible light that gets through, through the gaps and through the yarn itself. A lower figure means more glare reduction.
• Solar transmittance, reflectance and absorptance: what happens to the sun's whole energy at the fabric. For any one fabric the three add up to 100 percent. Reflected energy is turned back toward the window; absorbed energy heats the fabric.

The openness factor alone does not describe a fabric. One 3 percent screen fabric, in two colors, reads like this on its spec sheet (SheerWeave 2703 specification sheet, Hunter Douglas Architectural):

The light color reflects more of the sun's heat but lets more diffuse light through, so it gives more privacy and a less clear view. The dark face lets less light through and absorbs more heat, and because it is dark the eye looks past it to the brighter outside, so the view is clearer (View Through Simulation Tool, Hunter Douglas Architectural). In office research with Purdue University, Lutron found that two fabrics of the same openness can give very different glare, and that a smaller openness can still give more glare (Performance Fabric Research, 2015). That study was of offices, not homes.

Two cautions. Spec-sheet values are measured with the sun square to the glass, which it seldom is (IWFA Advanced Solar Control Education Guide 2026). And no maker or primary source we found pairs an openness with a window direction; the retailer charts that do are rules of thumb. How to choose one for your window is in Daylight, glare and darkness.

The AERC energy label

The Attachments Energy Rating Council is an independent nonprofit that rates window attachments (coverings, storm panels, films) for energy. A certified product's label carries two numbers (What Can You Learn from the AERC Energy Improvement Label?):

• Cool Climate rating: the council tells readers in the northern United States to use this one.
• Warm Climate rating: for readers in the southern United States (AERC FAQ).

How to read a number: a Cool Climate rating of 64 means the attachment saves 64 percent of the energy that would otherwise be lost through that window without it. Any rating above 0.00 saves energy compared with no attachment. Each product category has its own maximum improvement figure (the council's examples are 110 for storm windows in a cool climate and 15 for blinds), so compare a product with others of its kind. "Not Applicable" means the product is not recommended for energy improvement in that climate. The label also shows U-factor, solar heat gain coefficient, visible transmittance and air leakage, and an automated product shows a second rating for automated use.

What the label does not tell you: what you will save in your own home. In federal lab homes, cellular shades used the typical way (some up, some down) saved no significant heating energy, and the savings depended on opening and closing them by the sun (PNNL-27663, 2018). The Department of Energy's 2022 guide points readers to AERC ratings for shades (Energy Saver Guide), and Minnesota counts AERC-certified cellular shades in its energy program (DOE). ENERGY STAR does not certify curtains, blinds or shades; at the window it certifies low-e storm windows (ENERGY STAR, Storm Windows). The routine that makes any covering earn its rating is in Heat, cold and condensation.

The Best for Kids label

A voluntary certification run by the Window Covering Safety Council, the industry's safety body. A product carries it only if it has no cords, or has no operating cords and inner cords a child cannot reach, or has reachable inner cords that cannot form a hazardous loop. Products are tested by Bureau Veritas or Intertek. Products that rely on breakaway devices, tie-downs or cord cleats do not qualify (Best for Kids Certification Program). The council says the label was created in 2015 (WCSC FAQ on the 2022 standard). The program page still names the 2012 edition of the safety standard; the current edition is 2022.

What it does not tell you: that a product is safe in every room or every position, or that the rest of the room is. The label is about cords. Cribs, beds and climbable furniture near a window, and the window itself, are separate checks in Cords, children and fire.

The cord warning label

A warning label on a blind or shade means the product has cords. The industry's 2022 standard requires warning labels, in English and Spanish, on products that use a tension device on a cord loop or a retractable cord (ANSI/WCMA A100.1-2022), and the federal rule for window coverings requires an on-product label on both stock and custom products; the rule's status is set out in Cords, children and fire.

What to do when you see one, where a child lives or visits: the Consumer Product Safety Commission says cordless window coverings are the only way to remove the strangulation hazard, and that its interim steps (move cribs, beds and furniture away from windows, shorten pull cords, set cord stops, anchor loops to the floor or wall) reduce the hazard without removing it (CPSC, Window Covering Cords). Older blinds may carry no label; the commission says most blinds sold before November 2000 have inner cords a child can pull into a loop. List each covering on the cord sheet.

Fiber content and care

Curtains, casements and draperies sold in the United States carry a fiber-content label under the Textile Fiber Products Identification Act. Window coverings made mainly of slats, rods or strips of wood, metal, plastic or leather are excluded, so a blind or woven shade may have none (16 CFR Part 303). An extension bulletin of 1971 told shoppers the same about drapery fabric and ready-made draperies (University of Idaho, Be an "Aware" Shopper).

A care label is a different matter. The Federal Trade Commission's care-label rule covers clothing and fabric sold for sewing clothes; curtains and draperies are outside its definitions, so a curtain may come with no care instructions (16 CFR Part 423; that curtains fall outside it is our reading of the definitions). Ask the seller how to clean it, and test a hidden corner first. What each fiber does in sun and damp is in Fabrics and linings.

Ultraviolet percentages on film and fabric

Window films and screen fabrics often state how much ultraviolet they block: "up to 99 percent" in the window film trade body's words (IWFA FAQ), 97 percent on the 3 percent screen fabric above, and about 99, 97 and 95 percent at 1, 3 and 5 percent openness on one swatch card (Draper SheerWeave BASIC). The Skin Cancer Foundation's seal for film requires data showing 99 percent or more of UVA and UVB blocked (UV Window Film & Tint, updated December 2024).

Three things the percentage does not say:

• Which wavelengths. Ordinary window glass already stops most UVB; UVA passes through it. The National Park Service notes that a "98 percent" claim usually covers only the band from about 325 to 380 nanometers, while ultraviolet reaching a room through glass runs to 400 (Conserve O Gram 3/10, Choosing UV-Filtering Window Films, 2004).
• How much fading it prevents. Visible light fades color too. For light-sensitive colors, ultraviolet usually causes less than half of the fading and often only a tenth, and the only way to reduce fading is to reduce light (Canadian Conservation Institute, Light). The trade body says no film eliminates fading.
• What it does to the window. The same conservation body notes that film may void the warranty on sealed insulating glass; check yours, or ask the owner, before applying it.

Anchor, rod and track ratings

Anchor makers publish a figure in pounds. Read two things before you compare it with your curtain:

• Ultimate or working load. TOGGLER publishes ultimate loads, the load at which the anchor failed in independent lab tests, and says industry safety standards recommend one quarter of that as a safe working load (TOGGLER FAQs). Its 3/16 in SnapToggle has an ultimate tension of 238 lb in 1/2 in drywall, so a quarter is about 59 lb (SnapToggle technical sheet). ITW's E-Z Ancor sheet gives lab-average holding weights (40, 50 and 75 lb for the standard anchor in 3/8, 1/2 and 5/8 in board), does not say whether they are ultimate or working, and says to apply appropriate safety factors (E-Z Drywall Anchors technical sheet).
• The wall it was tested in. The figures are for a stated thickness of drywall (or block, or concrete), in good condition, with the load held close to the wall. The makers say age, moisture and condition change them. No anchor maker in this research publishes values for plaster and lath.

Rods and tracks have their own limits. Kirsch rates its Estate track at 64 lb maximum and 4 lb per foot, with brackets at each end and then every 48 in, closer for heavy drapery (Kirsch 2024 guide). A retailer's guide to Kirsch poles warns that anchors or molly bolts may not hold a wide span and says to use a stud (Drapery Rods Direct, Measuring & Selecting). The curtain weight and hardware calculator puts your curtain's weight beside these figures; it reports whether a published figure is above or below the estimate, and it does not say a wall will hold. How to find out what is behind the wall is in Hardware and installing.

NFPA 701 on a fabric sheet

A fabric or shade spec sheet may say the material passes NFPA 701. That is a fire test method for how flame spreads on textiles and films (NFPA 701, 2023 edition). Fire codes require it for curtains in assembly buildings and other public occupancies (City of Charleston, Decorative Materials in Assembly Occupancies); we found no source requiring it in a home. A pass does not make a curtain safe near a heater or candle: keep anything that can burn at least 3 ft from heat sources (U.S. Fire Administration).