Cast polyurethane elastomers and thermoplastic polyurethane (TPU) together cover the bulk of polymer specifications in consumer, industrial, and wearable electronics, with TPU dominating cases, cable jackets, and overmolds, and castable CPU/PU elastomers used where higher hardness, better dielectric, or tighter tolerances are required [S1][S4].
Selection in 2026 is driven less by marketing claims and more by three numbers: Shore A/D hardness, dielectric breakdown voltage, and continuous service temperature. Electronics designers should treat those as gating specs, with abrasion, UV stability, and flame rating as secondary filters [S2][S5].
Cast PU Elastomer vs TPU vs Other TPEs: Core Trade
Cast polyurethane elastomers are reaction-moulded from isocyanate (typically MDI or TDI) and a polyol such as PTMEG or PPG, with the isocyanate/polyol pair controlling the hard-segment content and therefore hardness, rebound, and upper service temperature [S5]. TPU is the thermoplastic counterpart: it is melt-processed, recyclable, and easier to colour or compound, but it carries a softer upper temperature limit than cast PU and cannot match a high-hardness cast grade on load-bearing or abrasion [S4]. Within the broader TPE family, styrenic block copolymers (SBS, SEBS), TPO, and TPV are cheaper but trade away either the tensile strength, the dielectric, or the chemical resistance that PU provides [S1]. For electronics, this trade usually resolves into a three-way pick: TPU for thin consumer parts, cast PU for industrial potting and gasketing, and silicone or EPDM only where PU cannot meet a temperature or UV target.
Hardness, Modulus, and Dielectric Targets for Enclosures
Polyurethane sheets and moulded parts can be formulated across the full low-density foam to hard solid range, with hardness typically quoted on the Shore A scale for flexible grades and Shore D for rigid structural parts [S5]. Consumer electronics case work and wearable components use TPU at the 70-95 Shore A band, where impact absorption coexists with mould detail, while connector grommets and industrial enclosures push into the 80 Shore A-50 Shore D range, where cut growth and compression set become the limiting properties [S4]. TPU is also noted for high tensile strength and good abrasion resistance, which is why it is specified for sheaths, plugs, and loose sockets in mobile-device accessories [S1][S4]. Dielectric strength should be confirmed in kV/mm at the actual part thickness: general-purpose cast PU elastomers typically fall in the 15-25 kV/mm range, and any grade carrying a UL 94 V-0 or V-2 listing is the default filter for potted assemblies.
Service Temperature, Flame, and Chemical Resistance
Cast polyester-based PU gives the best mechanicals and chemical resistance but hydrolyses in hot, humid conditions; polyether-based PU (PTMEG backbone) is the safer pick for outdoor enclosures and any electronics exposed to condensing humidity, because the ether linkage resists hydrolysis [S5]. Continuous service temperature for general-purpose TPU is usually capped around 80-90 °C, while cast PU elastomers can sustain 100-120 °C in dry air, with short excursions higher. For connector potting and PCB standoffs, the relevant call-outs are UL 94 V-0 at the specified wall thickness and a comparative tracking index (CTI) consistent with the PCB's voltage class, both of which need to be read from the grade datasheet rather than inferred from a generic TPU label. Aromatic TPU grades yellow under UV load; aliphatic TPU is the right answer for light-coloured or transparent device housings where photostability matters [S4].
Flexible Electronics, Wearables, and Conductive PU
Stretchable organic electronics, skin patches, and wearable sensors are an active research front in 2026, and polyurethane-based ionically conductive elastomers (ICEs) are one of the leading material platforms, combining ionic conductivity with the stretch and recovery that rigid elastomers cannot deliver [S3][S6]. Specialised TPU grades are used as the dielectric and substrate layers in stretchable devices, and the same chemistry supports in-mould antenna patterns and EMI gaskets once compounded with silver-coated fillers or carbon black [S1]. For human-machine interface sensors, ionic conductivity is the new gating spec, on top of the usual modulus, hysteresis, and biocompatibility checks; published ICE systems report gauge factors and stretch ratios that match skin-mounted use cases rather than moulded enclosures [S6]. Designers should keep the lab-scale ICE systems separated from production TPU: the former is a research platform, the latter is a commodity.
Selection Criteria for Electronics Design Engineers
Start with the four numbers that actually drive the decision: Shore A/D hardness, tensile and elongation, dielectric strength in kV/mm, and continuous service temperature, then add flame rating (UL 94 V-0/V-2 or IEC 60695), CTI for high-voltage assemblies, and any hydrolysis or UV exposure flag [S2][S4]. A practical decision tree for electronics: specify TPU at 80-95 Shore A for cases, straps, and cable jackets; specify cast polyether PU at 80 Shore A-50 Shore D for connector grommets, gaskets, and potting where humidity or chemical exposure is present; specify cast polyester PU only for indoor, dry, mechanically loaded parts where highest tensile and abrasion matter [S1][S5]. Treat silicone and EPDM as fall-backs, used only when the temperature or UV envelope exceeds what PU can deliver, and treat conductive TPE/PU compounds as a separate sub-spec on top of the base elastomer selection. The polyurethane elastomer reference page lists the standard property ranges and chemistry families this map leans on; for cabling, gasketing, and potting that also use foam-backed sheet stock, the polyurethane insulation entry covers the closed-cell and rigid-foam options that often sit under or over the elastomer layer.
Process and Tolerance Notes for Moulded Electronics Parts
TPU processes on standard injection moulding and extrusion equipment with melt temperatures typically 170-220 °C, and tolerates thin walls down to about 0.5-0.8 mm, which is why it has displaced PVC in many consumer cases and overmoulds [S1][S4]. Cast PU elastomers are processed as two-part liquid systems with either hot or room-temperature cures, giving tighter hardness control and better part-to-part repeatability for gaskets and pads, at the cost of longer cycle time. For both families, expect moulded-in colour to be easier with TPU and post-paint or pigmented systems to be more common on cast PU, and always validate dielectric, hardness, and tensile at the production cure cycle, not the lab mix [S5]. Two near-term signals worth tracking: wider commercial availability of aliphatic TPU at sub-premium pricing for transparent and UV-stable device housings, and the move of polyurethane elastomer ICE systems from research demos to qualified wearable-sensor SKUs, both of which would change the default grade on a 2026 electronics BOM [S3][S6].
For comparison with the automotive side of the same material family, where Shore hardness, fogging, and interior-VOC constraints are dominant, see the parallel polyurethane elastomer selection map for automotive manufacturing - the electronics map above applies the same four-number logic, but with dielectric and flame rating moved to the front of the spec.
Spec-level background on the components involved: pressure transmitter.