The short answer
Start with UV-stabilized ASA for molded-in color, PC/ASA for more heat and impact, or UV-stabilized or capped polycarbonate for clear parts and hard impacts. Weatherable PC/PBT suits housings near fuels and oils, glass-filled PBT suits small stiff parts, and electrical enclosures need FR grades with the right UL 94 and f1 listings. Pick the seal (EPDM, silicone or TPV) by compression set at the real temperature, and avoid unpainted ABS and standard PC in full sun.
This guide covers the housing and the gasket. For outdoor resins in general, see best plastics for outdoor use; for RTI, CTI and glow wire, see best plastic for electrical housings.
What an outdoor enclosure has to survive
- UV. Fading, chalking and yellowing first, then surface cracks and lost impact. See UV fading and yellowing.
- Solar heat. Dark housings in sun run far hotter than the air.
- Cold impact. A lid that survives a drop in summer can crack in winter. See best plastic for cold temperatures.
- Rain, ice and washdown. These load the gasket and closure more than the walls.
- Chemicals. Cleaners, fuels and oils can stress-crack PC, PC/ABS and ABS at snaps and bosses. See environmental stress cracking.
Ratings you will be asked about
- UL 746C outdoor suitability (f1, f2). A rating of the plastic grade. f1 means it met both the UV and the water exposure or immersion requirements of UL 746C: in outline, about 1,000 hours of xenon arc (or 720 hours of carbon arc) and 7 days in water at 70°C / 158°F, with flammability and mechanical properties compared before and after. f2 means only some of those tests were run, and outdoor suitability is left to the end-product evaluation. Recognition is grade-specific and color-specific, so check the grade’s listing on UL Product iQ for your color.
- UL 94 flame rating. Where the product standard calls for it; valid only at the listed thickness and colors. See UL 94 flame ratings explained and your part needs a flame rating.
- NEMA enclosure types. Defined in NEMA 250 and usually tested to UL 50E / CSA C22.2 No. 94.2. Outdoor types include 3R (rain, sleet, snow), 4 (windblown dust, hose-directed water), 4X (Type 4 plus corrosion resistance) and 6P (prolonged submersion).
- IP codes (IEC 60529). First digit for dust, second for water. IP66 means powerful water jets; IP67, temporary immersion (1 m for 30 minutes); IP68, continuous immersion under conditions the manufacturer states.
NEMA types and IP codes rate the finished enclosure as built, gasket and closure included; a resin grade has neither. The systems are not interchangeable: NEMA adds tests such as corrosion, icing and gasket aging, so an IP66 enclosure is not automatically Type 4X.
Housing resins compared
| Resin | Strengths outdoors | Watch out for | Typical uses |
|---|---|---|---|
| UV-stabilized ASA | Holds color and gloss without paint; molds much like ABS | HDT only about 80–95°C / 176–203°F, so check dark colors in sun; cold impact below ABS; few FR grades | Small housings and covers with molded-in color |
| PC/ASA | More heat and impact than ASA, with good weathering; FR grades exist | Costs more; hotter melt and more drying than ASA; can stress-crack with some cleaners | Electrical, telecom and equipment housings |
| PC, UV-stabilized or with a cap layer or coating | Highest impact; clear grades; HDT about 124–132°C / 255–270°F; some grades f1 | Yellows slowly even when stabilized; notch-sensitive, more so cold and in thick sections; stress-cracks with alkaline cleaners, solvents and fuels | Clear covers and windows, high-impact enclosures |
| FR PC or FR PC/ASA (electrical) | V-0, and 5VA in some grades, at stated thickness; some also carry f1 | Flame rating, f1 and colors are grade-specific; FR can change impact and weathering | Outdoor electrical enclosures and junction boxes |
| PC/PBT blend | Resists fuels, oils and many cleaners; tough in the cold; UV-stabilized grades run unpainted on vehicle exteriors | Opaque; shrinks differently from PC; both phases hydrolyze if molded wet | Vehicle- and equipment-mounted housings |
| Glass-filled PBT | Stiff, stable, low moisture uptake; thin-wall V-0 grades | Snaps take only about 1–2% strain; glass can show at the surface after weathering, so ask for UV-stabilized or black grades; hot, wet service needs hydrolysis-resistant grades | Connector and sensor bodies, small housings |
| UV-stabilized PP (low cost) | Lowest cost; chemical resistance; no drying; living hinges | Low heat and stiffness; creeps under gasket load; homopolymer is brittle near 0°C / 32°F, so use impact copolymer; hard to paint or bond | Low-cost boxes and hinged lids |
| Black HDPE or PP (carbon black) | Carbon black is the best UV screen; HDPE stays tough cold | Black only and runs hottest; low stiffness; creeps; needs good dispersion at the right loading | Large covers, utility boxes, rotomolded housings |
| ABS (painted or capped only) | Low cost, easy molding, good cold impact | Chalks, yellows and embrittles in sun; UV-stabilized ABS only slows it | Painted or capped parts only; otherwise use ASA |
General guidance; grades vary. Confirm with weathering data and the UL listing for the exact grade and color. More: ABS vs. ASA, ASA and SAN, polycarbonate and glass-filled PBT.
Color, heat and UV
- Dark colors run hotter. In full sun with little air movement, a dark surface can run tens of degrees hotter than the air, which on a hot day can approach the heat deflection of ASA or PC/ABS. Check the part temperature in a sunny test before you pick a resin by its heat rating. Check HDT against the real surface temperature.
- Carbon black gives the best UV protection when well dispersed, at the cost of a hotter part.
- Light colors run cooler but show change. Whites can yellow and bright organic colors fade fastest; pigment lightfastness matters as much as the resin.
- Ask for weathering data by grade and color: color change as Delta E (per ASTM D2244), gloss and impact retention after a stated xenon-arc exposure (ASTM G155 or ISO 4892-2). Accelerated hours do not convert to years, so compare grades under the same test.
Snap fits and lids outdoors
Producer guides give one-time allowable strains of roughly 4% for PC, 2.5% for PC/ABS and 1–2% for glass-filled grades; use about 60% of that for lids that open often, and more margin for cold service. PC is notch-sensitive, more so in the cold and in thick sections, so radius every snap root. Keep engaged snaps unstressed. Living hinges work only in PP; ASA and PC lids need pin hinges. See best plastic for snap fits and living hinges.
Choosing the seal
- TPV (EPDM/PP). Very good UV and ozone resistance, use from about −40 to 125°C / −40 to 257°F, and molds like a plastic. The usual thermoplastic gasket choice.
- EPDM (thermoset). Excellent weathering and generally the lowest set when hot. Made by rubber processors with a cure step, so it arrives as a finished gasket or cord.
- Silicone. The widest range, about −55 to 200°C / −67 to 392°F, with excellent UV and ozone resistance. Costs more; self-bonding LSR can be two-shot molded onto some thermoplastics.
- TPE-S (SEBS). Overmolds onto many substrates, but set climbs quickly when hot.
Judge each by compression set at the seal’s real peak temperature and time. See seals that take a set, TPV vs. other elastomers, TPV vs. EPDM and TPV vs. silicone.
Two-shot or separate gasket. Standard TPV bonds mainly to PP. On PC, PC/ASA or ASA housings, use a TPE grade made to bond to that substrate (usually a styrenic grade, with more set at temperature), add a mechanical lock, or fit a separate gasket in a groove. See overmold not bonding.
Processing notes
- Dry the housing resin. ASA at about 80–90°C / 176–194°F for 2–6 hours (cumulative maximum about 12 hours), PC at 120°C / 248°F for 2–4 hours to 0.02% or less, PBT at about 121°C / 250°F for 2–4 hours to 0.02%. Blends: follow the data sheet. See the resin drying guide.
- Do not overheat. Heat and long residence can use up stabilizer before the part sees the sun. Stay inside the processing parameters: ASA melt about 240–280°C / 464–536°F, PC about 280–345°C / 536–653°F.
- Control regrind. Each pass uses some stabilizer. Keep regrind at a tested level, never mix ABS regrind into outdoor ASA, and stay within UL 746D limits on recognized parts. See regrind limits by resin.
- Watch added color. A UV concentrate must be dosed evenly every shift, and adding your own color can take a part outside the grade’s UL listing.
What to send us
- The housing resin and grade you run now
- Sun exposure, temperature range and expected life
- Color and any weathering requirement
- UL 94 rating and thickness, f1 requirement, and the NEMA type or IP code the enclosure must meet
- Cleaners, fuels or chemicals it touches
- Gasket material, two-shot or separate
- Quantity and ship-to city
A polymer chemist reviews every request and checks the grade, its UL listing and weathering data before we quote. Every lot from our suppliers ships with a COA, and orders start at one gaylord. Samples of about 50 lb are available upon credit approval. We aim to send your quote within one to three business days.
Common questions
What is the best plastic for an outdoor electrical enclosure?
Usually a UV-stabilized, flame-retardant PC or PC/ASA grade with the UL 94 rating your product standard requires and an f1 rating under UL 746C in your color. Check the grade’s listing on UL Product iQ.
Is ABS OK outdoors?
Not on its own. The butadiene rubber in ABS breaks down in sunlight, so the part chalks, yellows and turns brittle; UV stabilizers only slow that. Painted or ASA-capped ABS works, and ASA, which molds much the same way, is the usual swap.
What does UL f1 mean?
f1 is a UL 746C outdoor suitability rating for a plastic grade: it met both the UV exposure and the water exposure or immersion requirements, with flammability and mechanical properties checked before and after. f2 means only some of those tests were run, and outdoor use is decided in the end-product evaluation. Both are listed by grade and color.
Does polycarbonate yellow outside?
Yes. Standard polycarbonate yellows, hazes and loses surface toughness in sunlight. UV-stabilized grades slow the change but do not stop it, and a UV-protective cap layer or coating lasts longest.
What gasket material is best for an outdoor enclosure?
EPDM, silicone and TPV all resist UV and ozone well. Silicone covers the widest temperature range, thermoset EPDM generally holds the lowest set when hot, and TPV molds like a plastic and suits two-shot seals on PP. Choose by compression set at the seal’s real peak temperature.
Does the resin give the enclosure its IP or NEMA rating?
No. NEMA enclosure types and IP codes (IEC 60529) rate the finished enclosure as built: walls, gasket, closure, fasteners and openings. A resin grade has no IP code or NEMA type of its own.
Tell us where the enclosure lives
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province