PES vs PSU Udel: Complete Engineering Comparison (2026) — Temperature, Strength, Cost

Which Material Should You Choose?Choose PES (Polyethersulfone) if:Higher temperature service (180°C), superior chemical resistance, aerospace interior components, medical devices requiring repeated steam sterilizationChoose PSU Udel (Polysulfone)...

PES (Polyethersulfone) and PSU (Polysulfone, Udel) are sibling amorphous thermoplastics in the sulfone polymer family. Both are transparent, amber-tinted, high-temperature engineering polymers with excellent hydrolytic stability and biocompatibility. The choice between them is primarily driven by temperature requirement and budget: PES offers 40°C higher glass transition temperature (225°C vs 185°C) and better chemical resistance, while PSU costs 30-50% less and has a longer track record of FDA and USP Class VI regulatory approvals.

When to choose PES: PES is specified when PSU's 160°C continuous service temperature is insufficient. With a Tg of 225°C and continuous service rating of 180°C, PES extends the amorphous sulfone performance envelope by 20°C. PES also has better chemical resistance than PSU — it withstands more aggressive solvents and has superior environmental stress crack resistance (ESCR). PES tensile strength of 83 MPa (vs PSU's 75 MPa) and flexural modulus of 2.6 GPa (vs PSU's 2.7 GPa) make it marginally stronger but equivalently stiff. PES is preferred for aerospace interior components (FAR 25.853 compliant), semiconductor wafer handling, and medical devices requiring repeated autoclave sterilization at 134°C. PES processes at melt temperatures of 340-380°C with mold temperatures of 120-160°C.

When to choose PSU: PSU (Udel) is the cost-effective workhorse of the sulfone family. At 30-50% lower cost than PES, PSU is the default choice for applications where 160°C continuous service is sufficient. PSU has an extensive regulatory track record — FDA-compliant for repeated food contact, USP Class VI and ISO 10993 biocompatible, and NSF-61 certified for drinking water contact. This makes PSU the standard material for hot water plumbing fittings, food service equipment (coffee machine brew chambers, milk steaming wands), dialyzer housings, and surgical instrument handles. PSU's transparency (amber tint) and 1000+ autoclave cycle tolerance make it ideal for medical devices requiring visual inspection of internal fluids. PSU processes at melt temperatures of 330-380°C with mold temperatures of 80-150°C.

Thermal performance comparison: The 40°C Tg advantage of PES translates directly to higher HDT — PES has HDT of 204°C at 1.82 MPa vs PSU's 174°C. For applications with sustained service above 160°C, PES is required. For intermittent temperature spikes (e.g., solder reflow at 260°C), both materials survive brief excursions, but PES retains more mechanical integrity during the spike. Below 150°C continuous, PSU is the more economical choice with equivalent performance.

Chemical resistance comparison: Both polymers share the sulfone family's vulnerability to polar organic solvents (ketones, esters, chlorinated solvents). PES has measurably better ESCR than PSU, tolerating higher stress levels in the presence of these solvents before cracking initiates. For applications with intermittent solvent exposure (e.g., medical devices cleaned with isopropyl alcohol), PES offers a wider safety margin. For continuous solvent exposure, neither material is suitable — upgrade to PPSU (Radel) which has the best ESCR in the sulfone family.

Comparison at a Glance

Related Diagnostics & Materials

References & Industry Standards

• ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
• UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
• MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
• ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org