Plastic vs Cast-Iron Truncated Dome (2026)

A plastic truncated dome is a fiber-reinforced polymer or polymer-concrete panel with the dome geometry molded into the surface, while a cast-iron truncated dome is a powder-coated metal plate, typically installed in a replaceable frame, with the domes cast as part of the iron itself. Both meet ADA Standards 705.1 dome dimensions and 705.2 contrast when correctly specified, but they diverge sharply on lifespan, snowplow tolerance, and how the dome surface holds 70 percent contrast over time.

This guide weighs both materials on the wear performance ADA 705.5 requires, the cost lines that drive a purchase, and the substrate and climate conditions that should steer the spec.

What Is a Plastic Truncated Dome?

A plastic truncated dome is a composite panel molded from fiber-reinforced polymer (typically a glass-reinforced thermoset), polymer concrete, or recycled polymer. Manufacturers including ADA Solutions, Armor-Tile, and Detectable Warning Systems publish ADA 705 spec sheets and ASTM E303 slip resistance testing on their panels.

Plastic panels arrive in fixed sizes (24 inches by 24 inches up through 36 inches by 60 inches) and are installed as cast-in-place or surface-applied units. They are the dominant product family in the U.S. by panel count because they cost less per square foot than cast iron and meet ADA 705 cleanly out of the box.

Are plastic truncated domes durable?

Plastic panels are durable in pedestrian-only environments. They wear well against shoe traffic, mobility devices, and dolly carts. They are vulnerable to snowplow blade strikes, vehicle wheel impact at high deflection angles, and UV-driven contrast fade over 7 to 10 years. The polymer-concrete sub-family resists those failure modes better than thermoset alone but still trails cast iron.

What Is a Cast-Iron Truncated Dome?

A cast-iron truncated dome is a structural iron plate with the truncated-dome geometry cast directly into the metal. Manufacturers including East Jordan Iron Works and Neenah produce panels in 24-inch by 24-inch up through 36-inch by 36-inch sizes, typically in replaceable-frame systems where the iron plate bolts into a stainless-steel-anchored carrier.

Cast iron resists impact, abrasion, and freeze-thaw cycling that destroys most polymer products. The trade-off is initial cost, weight (a 24-inch by 24-inch plate runs 35 to 60 pounds), and the structural anchoring required to support the load.

Does cast iron meet ADA 705 contrast?

Yes. Manufacturers powder-coat cast-iron panels in federal yellow (RAL 1023), brick red, or black to deliver ADA 705.2 contrast against the adjacent walking surface. The powder-coat finish holds color through year 15 to 20 in typical conditions. Edge wear can expose the bare iron, which fails contrast in those localized spots and triggers the 705.5 wear replacement.

Side-by-Side Spec Comparison

| Spec | Plastic (composite) | Plastic (polymer concrete) | Cast iron | |------|--------------------|--------------------------|----------|

When to Choose Plastic

Plastic truncated domes are the right call in most pedestrian-only commercial settings.

Is the curb cut indoor or covered?

A covered curb cut at a hospital entrance or a parking-garage transition has no UV exposure and no plow exposure. A composite plastic panel can hold ADA 705 compliance for 12 to 15 years in those conditions. Cast iron is overspecified.

Is the substrate concrete and the project a single curb cut?

A standalone retail entrance with one curb cut and pedestrian traffic only is the textbook composite-plastic application. Initial cost is low, install is straightforward, and the panel will outlast the typical commercial lease cycle.

Is the property short-hold (5 to 7 years)?

Owners who plan to sell or redevelop inside 7 years rarely capture the lifecycle savings of cast iron. Plastic clears the ADA 705 threshold today and lasts long enough to clear the hold.

When to Choose Cast Iron

Cast iron is the right call in four conditions.

Is the curb cut plowed in winter?

Bend, La Grande, Pendleton, Hood River, and other snowbelt jurisdictions wear out plastic panels at the leading edge from repeated plow contact. Cast-iron plates absorb the strike and stay in place. Cojo replaced four Bend transit-stop curb-cut composites in February 2026 with replaceable cast-iron systems for that exact reason.

Is the location on a heavy-vehicle path?

Loading-dock approaches, drive-thru curb cuts, and parking-lot edges where vehicles regularly cross at high deflection angles are cast-iron territory. Polymer panels split. Iron does not.

Is this a long-hold or public-bid project with a long warranty?

Public bids that require a 15 plus year service life on the dome surface usually default to cast iron because polymer manufacturers do not publish a matching warranty. The lifecycle math also favors iron once the horizon clears 12 years.

Is the spec sheet calling for AASHTO M306 load rating?

That spec only exists in cast-iron product lines because plastic panels do not meet the load class. If the architect or engineer specified M306, plastic is not on the table.

Cost Comparison

Industry Baseline Range

Current Market Reality

Cast-iron prices climbed 18 to 24 percent in 2025 on raw-iron and powder-coat surcharges. Polymer-concrete prices climbed 12 to 16 percent on resin and aggregate inputs. Composite panels were the smallest 2025 price increase but face the biggest 2026 risk because UV-stabilizer additives are tightening on supply. ADA 705 inspection rigor is climbing across all product lines, which extends layout time and labor cost regardless of material.

Compliance Disclaimer

This article reflects ADA Standards for Accessible Design as of 2026-05-07 and product spec sheets current at publication. Always verify current dimensions, contrast thresholds, and placement requirements with your local jurisdiction and the U.S. Access Board before issuing a final spec. Federal guidance under 36 CFR Part 1191 controls when state or local rules conflict. Material selection alone does not satisfy ADA compliance — installation geometry and 705.2 contrast verification at install are equally controlling.

Sources

• ADA Standards for Accessible Design, Section 705 Detectable Warnings, U.S. Access Board, https://www.access-board.gov/ada/
• 36 CFR Part 1191, Americans with Disabilities Act Accessibility Guidelines, https://www.ecfr.gov/current/title-36/chapter-XI/part-1191
• FHWA Accessibility Resource Library, https://highways.dot.gov/civil-rights/programs/ada/accessibility-resource-library
• Oregon Department of Transportation, ADA Curb Ramp Design Guide, https://www.oregon.gov/odot/engineering/pages/ada.aspx

From Cojo's Crew

On a 14,000-square-foot Salem retail center in March 2026, the owner specified composite plastic for 6 retrofit curb cuts and cast iron for the 2 loading-dock approaches. Three months later both product families are still ADA 705 compliant on geometry and contrast. The right answer was not one material — it was matching the material to the failure mode the curb cut would actually face. That is the discipline this comparison exists to enforce.