Best Plastic for Outdoor Extruded Profiles and Sheet

The short answer

For most colored outdoor profiles and sheet, the best value is a coextruded part: a thin weatherable cap of ASA, acrylic (PMMA) or PVDF over a lower-cost substrate such as rigid PVC or ABS. Rigid PVC with a PVC capstock suits light colors. Mid to dark colors hold better under an ASA or acrylic cap with low heat-build pigments. Use solid ASA, or ASA/PC for more heat, where the whole profile must weather. For clear, impact-resistant sheet, use polycarbonate with a coextruded UV layer. For boards and lumber, use black or HALS-stabilized HDPE. Consider PVDF where long-term color hold justifies the cost. Judge grades on natural exposure and on color, gloss and impact retention, not on accelerated hours alone.

Quick quote

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Paste it as written. A polymer chemist will tell you which grade it calls for, suggest equivalents and quote it by email.

Why extruded outdoor parts are a special case

Profiles, siding, trim, fencing and sheet differ from molded outdoor parts in four ways that drive resin choice:

Most of the part never sees the sun. Only the face weathers, so a thin cap layer can carry the UV load while a cheaper substrate carries the structure.
Long lengths move. Thermal expansion over a 3 m (10 ft) length is measured in millimeters, and the profile has to be fastened to allow for it.
Dark faces run hot. A classic Q-Lab paper reports that 70–80°C is common on dark, insulated horizontal surfaces, and that white paints typically peak 10–15°C cooler than black. That is at or above the range where rigid PVC softens (glass transition about 74–82°C, depending on the source).
Color is the spec. Most extruded outdoor products fail on fade, chalking or yellowing long before they fail structurally.

For outdoor plastics in general, see best plastics for outdoor use. For molded housings, see best plastic for outdoor enclosures.

Outdoor extrusion resins compared

Resin or structure	How it is used	UV and color hold	Heat (typical)	Watch for
Rigid PVC, weatherable compound with PVC capstock	Siding, soffit, trim, fencing and window profiles; TiO2-rich cap over a low-cost substrate	Good in light colors; ages by yellowing (dehydrochlorination), then fade and chalking	Tg about 74–82°C (165–180°F), depending on the source; HDT is compound-specific, so check the sheet	Dark colors can heat past PVC’s usable range and distort; makers use IR-reflective pigments, limit colors or move to CPVC or other caps
PVC with ASA or acrylic capstock	Mid- to dark-color siding, soffit, roofing and window profiles	Better color hold than PVC capstock in mid to dark colors	Substrate still sets the heat limit	Cap and substrate expand at different rates, which builds stress in the part
ASA, solid or as a cap	Trim, profiles and sheet in molded-in color; capstock over PVC or ABS	Very good; holds color and gloss far better than ABS	Grade-specific; check HDT and Vicat on the current sheet. One siding patent puts ASA’s glass transition near 96°C (205°F), against about 74°C (165°F) for PVC	Expands more than PVC, per the same patent; use the expansion value on your grade’s current sheet; choose weatherable colors
ASA/PC	Profiles and sheet that need more heat and impact than ASA	Check weathering data for the exact grade	Higher than ASA; grade-specific	Needs drying; the PC phase can stress-crack with some chemicals; confirm cost against ASA
Acrylic (PMMA) capstock	Cap over ABS, PC/ABS, PC, PVC, CPVC, cellular PVC, HIPS and wood-plastic composites	Excellent; one producer says its acrylic resins remain virtually unchanged after long-term accelerated and outdoor weathering	Substrate sets the limit	Less impact-resistant than PC (impact-modified cap grades exist); HIPS needs a cap grade with an adhesion promoter
PVDF cap or coating	Coextruded over PVC with a tie layer, or applied as a PVDF-based coating on extruded PVC	Very good; a siding patent describes PVDF (Kynar 500) coatings as giving color retention, gloss retention and chalk resistance	Substrate sets the limit	PVDF needs a tie layer to bond to PVC in coextrusion; confirm cost against acrylic or ASA
Polycarbonate with coextruded UV layer	Solid and multiwall sheet for glazing, skylights and covers	Good with the cap facing out; uncapped PC yellows	Maximum service temperature without load 120°C (current Exolon multi UV multiwall sheets)	Install UV side out; expansion about 0.065 mm/m·°C; fire behavior can change with weathering
UV-stabilized HDPE or PP	Marine board, outdoor furniture, plastic lumber, sheet	Good with carbon black or HALS; unstabilized grades turn brittle	Lower stiffness and heat than the styrenics above	Creep and sag between supports; high expansion; HALS do not work in PVC

Values from current producer data sheets, patents and published references for single products. Weathering depends on the grade, pigment, color, cap thickness and climate. Confirm with the grade’s weathering data.

The capstock approach: a thin weatherable layer over a cheaper core

Most vinyl siding and many profiles are coextruded in two layers. NIST describes siding as a low-cost PVC substrate with a thin, TiO2-rich weatherable capstock of PVC, PMMA, ASA or blends of these.

Cap thickness. On one commercial siding, NIST measured an ASA cap of about 40 µm. A siding patent describes an outer layer of about 0.003–0.005 in (about 76–127 µm). Ask your cap supplier for the minimum that holds color on your profile, and check coverage on edges and corners.
What bonds to what. ASA is coextruded over PVC (NIST’s siding sample had an ASA cap on U-PVC). Acrylic cap grades are made for ABS, PC/ABS, PC, PVC, CPVC, cellular PVC and wood-plastic composites, and coextrude without adhesives or primers. HIPS needs an acrylic grade with an adhesion promoter. PVDF coextrusion over PVC has used a tie layer (an Arkema patent describes PVC / tie resin / PVDF made on a coextrusion line).
Processing. Acrylic capstocks process at temperatures similar to PVC. Acrylic powders can also be compounded into a PVC capstock to raise weathering toward an all-acrylic cap.
Stress between layers. PVC and ASA have different glass transition temperatures and expansion rates. One siding patent notes that heating and cooling in production and in service build stresses that can permanently deform the part. Keep the cap thin and the profile balanced.
Cost logic. The cap is a small share of the weight, so a premium cap resin adds less to part cost than making the whole profile from it would.

Heat sag, expansion and dark colors

Check heat against the real surface temperature. A dark profile at 70–80°C is at or above the range where rigid PVC softens (glass transition about 74–82°C). Solid ASA or ASA/PC can give more margin (one siding patent puts ASA’s glass transition near 96°C); compare the exact grade’s HDT or Vicat with the expected surface temperature. See HDT vs. continuous use temperature.
Low heat-build pigments. One siding patent notes that most makers use IR-reflective pigments or limit dark colors. IR-reflective pigments and low heat-build capstocks lower surface temperature in dark colors. ASTM D4803 compares heat build-up against black. It gives a relative value and does not predict the actual installed temperature.
Foam backing and insulation. One siding patent reports foam-backed siding running about 15–20°F hotter than hollow-back product.
Expansion, worked example. At 0.065 mm/m·°C (current Exolon multiwall PC sheet), a 3 m PC sheet grows about 10 mm over a 50°C swing. ASA expands more than PVC; run the same calculation with the expansion value on your grade’s current sheet. Slot the fastener holes and leave end gaps.
Sag in polyolefins. HDPE and PP boards creep between supports, more in heat and dark colors. Close the support spacing rather than relying on the data-sheet modulus.

Weathering tests: what the numbers do and do not mean

Test	What it does	How to use it
ASTM G154 (fluorescent UV)	UV lamps with condensation; Cycle 1 alternates 8 h of UV with 4 h of condensation	Ranking materials; fluorescent UV matched outdoor results better than xenon in one Q-Lab study on capped PVC siding, using a modified cycle
ASTM G155 (xenon arc)	Full-spectrum light with water spray; Cycle 1 runs 102 min of light and 18 min of light with spray at a 63°C black panel	Color and appearance screening; no direct correlation to years outdoors
Natural exposure (South Florida, Arizona, northern sites)	Real sun, heat and moisture, often at 45° facing south	The reference. The Vinyl Siding Institute certifies colors after two years in Miami, Phoenix and Cleveland
Color change, ASTM D2244	Measures color difference (ΔE or a color-tolerance ellipsoid)	Set a limit after a stated exposure. ASTM D6864 and D7251 covered siding color retention but are listed by ASTM as withdrawn in 2018, so ask which current spec or certification applies
Gloss and impact retention	Gloss and impact measured after exposure, compared to unexposed	Ask for retained values, not just initial ones; surface embrittlement shows up in impact first

Neither G154 nor G155 sets a pass limit on its own. ICC-ES notes G155 is meant to be paired with a method that sets the exposure and how changes are judged. Use them to compare materials side by side, not to convert hours into years.
Acceleration varies by material. A classic Q-Lab paper (1977, on coatings) found lab-to-Florida ratios from about 8:1 for the most durable coatings to 25:1 for the least durable. One conversion factor does not fit all grades.
Climate matters. In VSI’s program, Cleveland produced more color change than Florida or Arizona for its products, while Arizona yellowed white specimens most.
Product specs. ASTM D3679 covers rigid PVC siding and ASTM D7254 covers polypropylene siding.

Decision table

Product	First choice	Why
Siding, soffit and trim in light colors	Rigid PVC with PVC capstock	Lowest cost; proven color hold in light colors
Siding, window and trim profiles in mid to dark colors	PVC substrate with ASA or acrylic cap, low heat-build pigments	Better fade resistance; controls heat build-up
Profiles that must weather all the way through, or run hotter	Solid ASA, or ASA/PC	Weathers without a cap; can give more heat margin than PVC (check the grade)
Colored sheet for thermoformed exterior panels and covers	ABS with ASA or acrylic cap	ABS toughness and formability with a weatherable face
Clear glazing, skylights and covers that get hit	PC sheet with coextruded UV layer	Far tougher than acrylic; cap slows yellowing
Clear sheet where impact is low and clarity must last	Acrylic	Stays clear without a cap; see PC vs. acrylic
Marine board, outdoor furniture, plastic lumber	UV-stabilized HDPE (black or HALS)	Tough, water- and rot-proof, color molded in
Architectural profiles where color must hold longest	PVDF cap or coating over PVC	Color and gloss retention reported for PVDF coatings; justify the cost on long-life products

Starting points. Color, wall, span, climate and warranty terms change the answer.

What to put on your RFQ

Structure. Solid or coextruded; cap resin and target cap thickness; substrate resin.
Color and heat. Color code or match, and whether low heat-build or IR-reflective pigments are required.
Weathering evidence. Natural exposure data (site, years, ΔE limit) or the accelerated cycle you accept, with retained gloss and impact.
Heat. HDT or Vicat with the method, compared against the expected surface temperature.
Product spec. ASTM D3679, D7254 or your customer’s spec, if one applies.
Processing. Extrusion or coextrusion, melt flow or K-value for PVC, drying needs (ASA and PC need drying), and regrind limits.
Volume. Annual pounds and release size, by layer.

A polymer chemist reviews every request and checks the cap and substrate pairing before we quote. Every prime lot ships with a supplier COA, from one gaylord to a railcar.

Common questions

What is the most UV-resistant plastic for extruded profiles?

PVDF and acrylic (PMMA) caps are the usual choices where color hold matters most, with ASA widely used for molded-in color. Because only the face weathers, they are usually used as a thin coextruded cap over PVC or ABS rather than as the whole profile.

Is ASA better than PVC for outdoor profiles?

ASA holds mid and dark colors better and can give more heat margin: one siding patent puts ASA's glass transition near 96°C (205°F), against about 74°C (165°F) for PVC; other references put PVC near 82°C. Check the HDT or Vicat on the exact grade. PVC costs less and holds light colors well. Many products combine them as an ASA cap over a PVC substrate.

How many hours of QUV or xenon equal a year in Florida?

There is no fixed conversion. Acceleration ratios vary by material, from about 8:1 to 25:1 in one classic Q-Lab study, and xenon correlated poorly with outdoor results for capped PVC siding in another. Use accelerated tests to rank materials and natural exposure to confirm.

Why do dark PVC profiles warp in the sun?

Dark surfaces can reach 70–80°C, which is at or above the range where rigid PVC softens. Makers use IR-reflective pigments, low heat-build caps, ASA or acrylic capstock, or CPVC, and limit dark colors on plain PVC.

Sources

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