Polysulfone Plastic — Udel PSU & Radel PPSU Guide

Polysulfone plastic covers two closely related engineering thermoplastics — Udel PSU (polysulfone) and Radel PPSU (polyphenylsulfone) — both prized for their amber transparency, hydrolytic stability, and ability to withstand repeated steam sterilization without degrading. PSU handles continuous service to 300°F; PPSU raises that ceiling to 350°F with a documented tolerance for 1,000+ autoclave cycles. Both materials occupy the gap between general-purpose polycarbonate and premium PEEK: higher heat and chemical resistance than PC, lower cost than PEEK, with a sterilization track record that neither can match.

At a glance:

• Udel PSU: continuous use 300°F (149°C), Tg 374°F (190°C), tensile strength 10,200 psi
• Radel PPSU: continuous use 350°F (177°C), Tg 428°F (220°C), tensile strength 10,500 psi, 1,000+ steam autoclave cycles
• Both available in sheet and rod, natural transparent amber color
• FDA 21 CFR 177.1655 compliant (PSU/PPSU), USP Class VI, NSF 51
• Hydrolytically stable — no strength loss from repeated steam, hot water, or chemical disinfectants
• Key brands: Solvay Udel / Radel, BASF Ultrason
• Suitable alternatives to polycarbonate where sterilization or hot water exposure is required

What Is Polysulfone?

Polysulfone is an amorphous thermoplastic defined by sulfone linkages (–SO₂–) in its backbone chain. These linkages, flanked by aromatic rings, provide exceptional rigidity at elevated temperatures and resistance to oxidative degradation — the same chemistry that makes polysulfone unique among transparent engineering plastics.

PSU vs. PPSU — Same Family, Different Performance Tier

Udel PSU (polysulfone) is the base grade. It was commercialized in the 1960s and remains the cost-effective choice when service temperatures stay below 300°F and sterilization cycles are moderate. Radel PPSU (polyphenylsulfone) adds additional phenyl groups to the backbone, increasing toughness, heat resistance, and hydrolytic stability substantially. PPSU handles 1,000+ steam autoclave cycles at 270°F (132°C) with virtually no property loss, making it the preferred material for reusable surgical trays, dental cassettes, and animal cage components that cycle through institutional autoclaves daily.

Appearance and Optical Properties

Both grades are naturally transparent amber — not clear, but translucent enough to inspect contents in medical trays or fluid-handling components. The amber tint deepens slightly with PPSU. Neither grade is available in standard opaque colors; the natural amber is an inherent property of the sulfone backbone chemistry.

Key Mechanical and Thermal Properties

Polysulfone offers a balanced property profile that outperforms polycarbonate in temperature and chemical exposure while remaining significantly easier to machine than PEEK.

PPSU is meaningfully tougher — its notched Izod impact value is roughly twice PSU's, which translates to better crack resistance during mechanical sterilization loading and unloading. For most structural machined parts, PSU's modulus and strength are more than adequate.

Hydrolytic Stability — The Critical Differentiator

Unlike polycarbonate, which degrades measurably with steam and hot-water exposure, both PSU and PPSU maintain their mechanical properties through repeated wet sterilization. Testing by Solvay shows PPSU parts retaining over 95% of tensile strength after 1,000 steam autoclave cycles at 270°F. This stability comes from the sulfone group's inherent resistance to hydrolysis — the ester linkages in polycarbonate that hydrolyze under steam are simply absent from the polysulfone structure.

Chemical Resistance

Polysulfone is broadly resistant to dilute acids, bases, and aliphatic hydrocarbons. It withstands common hospital disinfectants — quaternary ammonium compounds, iodophors, and hydrogen peroxide vapors — without crazing or cracking.

What to Avoid

Concentrated organic solvents attack polysulfone aggressively. Chlorinated solvents (methylene chloride, chloroform), ketones (MEK, acetone), and aromatic hydrocarbons (toluene, xylene) will dissolve or severely craze both PSU and PPSU. Avoid chlorinated coolants during machining — use water-soluble or air-cooling approaches instead.

Strong oxidizing acids (concentrated nitric or sulfuric) and polar aprotic solvents also attack polysulfone. See the full chemical resistance table in our properties guide for a detailed compatibility list.

Grades: Udel PSU vs. Radel PPSU

Choosing between PSU and PPSU comes down to sterilization intensity and budget.

Udel PSU — Standard Grade

Udel PSU from Solvay (formerly Union Carbide) is the original commercial polysulfone. BASF markets a comparable resin as Ultrason S. PSU suits applications requiring intermittent autoclave sterilization (fewer than 100–200 cycles) or continuous hot-water service up to 300°F. It costs less than PPSU and is available in a wider range of stock thicknesses.

Radel PPSU — High-Cycle Sterilization Grade

Radel PPSU is the choice when parts must survive daily institutional autoclave cycling over a multi-year service life. Dental cassettes, surgical instrument trays, and animal cage components made from PPSU routinely reach 500–1,000 sterilization cycles before showing any visible degradation. PPSU also offers better impact resistance for parts that sustain drops or rough handling in clinical environments.

For a detailed grade comparison with a sterilization-cycle picker, see the polysulfone grades guide.

Applications

Polysulfone's combination of sterilization tolerance, dimensional stability, and FDA compliance makes it a standard material in several industries:

Medical and Dental

Reusable instrument trays, sterilization cassettes, dental instrument holders, and fluid management components in surgical suites. PPSU is preferred for highest-cycle applications; PSU is used for components that autoclave less frequently.

Food Processing and Dairy

Steam-cleanable contact surfaces, dairy pipeline fittings, food-service equipment parts where hot-water and chemical sanitizer resistance is required. Both PSU and PPSU comply with FDA 21 CFR 177.1655 for food-contact use.

Plumbing and Hot Water Systems

PSU is approved for potable water contact (NSF 14/61) and resists degradation from chloramines present in municipal water supplies. Hot-water valve bodies, pipe fittings, and flow components in high-temperature systems benefit from PSU's dimensional stability up to 300°F.

Laboratory and Animal Research

Autoclavable animal cage components — water bottles, cage tops, feeding accessories — have been made from PPSU for decades because of its daily sterilization tolerance and resistance to ammonia in bedding environments.

See the full applications overview for industry-specific details.

How Polysulfone Compares to Alternatives

Polysulfone occupies a specific niche. Understanding where it sits relative to competing materials helps narrow material selection quickly.

Against polycarbonate, polysulfone wins on temperature ceiling and sterilization tolerance at a modest cost premium. Against Ultem / PEI, PSU costs less and handles food contact more broadly, though Ultem offers higher continuous temperature and better flame performance. Against PEEK, polysulfone is significantly more economical and serves adequately in medical and food applications that don't require PEEK's exceptional chemical resistance or 480°F service rating.

See the comparisons index for full side-by-side details, including the polycarbonate vs. polysulfone comparison.

Stock Forms and Specifications

Polysulfone is stocked in sheet and rod forms in natural amber. Standard sheet sizes run from 12"×24" up to 24"×48", in thicknesses from 1/8" through 4". Rod diameters range from 1/4" to 4" diameter.

Tolerances on extruded rod and compression-molded sheet follow ASTM D6098 for dimensional accuracy. Thickness tolerance on sheet is typically ±10% for stock items. For tighter requirements, order oversized and machine to finish dimensions after stress-relief annealing.

For complete size charts, see polysulfone specifications.

Machining Polysulfone

Both PSU and PPSU machine well on conventional metalworking equipment. Key considerations:

• Anneal before machining to relieve molding or extrusion stresses — 250–300°F for 2–4 hours is typical
• Use sharp carbide tooling to minimize heat buildup at the cutting edge
• Light feed rates prevent deflection and surface heat
• No chlorinated cutting fluids — use compressed air, water-soluble coolants, or dry cutting
• Parts are prone to stress-cracking if machined with dull tools or inadequate chip clearance

Detailed feeds, speeds, and tool geometry recommendations are in the machining guide.

FDA, USP, and Regulatory Compliance

Both PSU and PPSU carry the compliance credentials required for medical and food applications:

• FDA 21 CFR 177.1655 — polysulfone for food-contact use
• USP Class VI — biocompatibility for medical devices
• NSF 51 — food equipment materials
• NSF 14/61 — potable water contact (PSU)
• Autoclave-compatible (steam sterilization at 250–270°F / 121–132°C)

Full regulatory details and certification context are in the FDA and food-grade compliance guide.

Forms, Colors, and Manufacturers

Polysulfone is stocked in two basic forms — sheet and rod — in natural amber. Custom tube, square bar, or other profiles are not standard stock items and require custom extrusion.

Sheet: Compression-molded or extruded flat panels, 12"×24" and 24"×48" standard, thicknesses from 1/8" through 4". Sheet is the primary form for machined flat components: tray bodies, panels, spacers, and flat gaskets.

Rod: Extruded round rod, 1/4" through 4" diameter in 4-foot and 6-foot lengths. Rod is used for turned components: fittings, connectors, valve seats, bushing blanks, and threaded fastener bodies.

Manufacturers: Solvay is the dominant producer of polysulfone shapes, supplying Udel PSU (P-1700 series) and Radel PPSU (R-5100 series) as the industry reference resins. BASF markets equivalent resins as Ultrason S (PSU) and Ultrason P (PPSU). Specifications referencing either brand or the ASTM D6098/D6107 standard are interchangeable at the resin level.

Dimensional Stability and Design Considerations

Polysulfone is an amorphous thermoplastic with no crystalline transition — it softens gradually above its Tg rather than exhibiting the sharp melt point of semicrystalline materials like PEEK or nylon. This amorphous structure gives PSU and PPSU excellent dimensional stability below their Tg values but means they are more susceptible to stress cracking from solvents and aggressive chemicals than semicrystalline alternatives.

The coefficient of thermal expansion (CTE) for PSU is 31 × 10⁻⁶ in/in/°F — higher than steel (~6.5 × 10⁻⁶) but comparable to other engineering thermoplastics. For assemblies with metal components cycling through autoclave temperatures, design clearances must account for differential thermal expansion between polysulfone parts and stainless steel fasteners or inserts.

Low water absorption (0.30% for PSU, 0.37% for PPSU at 24-hour immersion) means dimensional change from moisture uptake is minimal — far less than nylon (2–9% absorption) and comparable to polycarbonate. This makes polysulfone dimensionally predictable in wet environments where nylon would swell and affect fits.

Get Polysulfone Sheet and Rod

Both Udel PSU and Radel PPSU are stocked in sheet and rod. Request a quote with your dimensions, grade preference, and quantity for same-week lead times on standard sizes.

More related guides

Cross-cluster suggestions to help shoppers and engineers explore adjacent topics:

Applications

• Medical Sterilization

Industries

• Medical

Compare to other materials

• Ultem Vs. Polysulfone
• Polysulfone Vs. Polycarbonate

Frequently asked questions — Polysulfone FAQ