Power Unit Materials: Rules Inside the PU Perimeter

The power unit perimeter in Formula 1 is a concept created to manage the materials and design freedom inside the engine, turbocharger, MGU-K, energy store, and their associated systems separately from the rest of the car. Within that boundary, Article 15 applies a stricter and more granular set of material rules than those governing chassis and aerodynamic structures. The restrictions extend from broad category bans at the general level down to component-specific prescriptions that tell engineers not just what material class is permitted, but in some cases the exact alloy and manufacturing method required.

General Prohibitions Inside the PU Perimeter

The Materials Excluded at the Boundary

Article 15.7.1 lists the material classes prohibited inside the PU perimeter. Magnesium-based alloys are banned, addressing the fire risk that comes from a material that burns intensely and resists conventional extinguishing in an environment surrounded by fuel, oil, and hydraulic systems operating at elevated temperatures. Metal Matrix Composites are banned for applications where the composite volume fraction exceeds 2.0% volume for volume, targeting the class of MMC that delivers meaningful stiffness or thermal performance gains over unreinforced alloys. Intermetallic alloys are prohibited, removing ordered atomic structure materials whose high-temperature stiffness properties would otherwise find application in turbine-adjacent components.

Ceramics and ceramic matrix composites are prohibited inside the perimeter under 15.7.1(h), even though carbon-carbon composites and specific monolithic ceramics appear in the Article 15.5 exceptions list for brake friction materials and similar applications outside the perimeter. The reasoning inside the perimeter is the same as for intermetallics: brittle fracture behavior in a high-thermal-cycling, high-vibration, high-mechanical-shock environment creates unpredictable failure modes that the FIA is unwilling to permit in components where failure would have immediate consequences for the power unit and potentially the driver.

Aluminium alloys containing more than 1.0% lithium by weight are also banned inside the perimeter, tightening the restriction compared to the outside-perimeter rules which permit lithium contents up to 1.0% for wrought alloys and up to 2.5% in specific alloy designations. Similarly, aluminium alloys containing more than 1.0% silver are prohibited inside the PU. Both restrictions target alloy systems whose exceptional specific strength could otherwise be exploited for PU components where weight reduction is a competitive variable.

Beryllium and Precious Metal Limits

The beryllium threshold inside the PU perimeter is stricter than outside. Copper-based alloys above 2.2% beryllium are prohibited under Article 15.7.1(e), compared to the 2.5% limit applying outside the perimeter for the same alloy family. More significantly, any alloy class other than copper that contains more than 0.25% beryllium is banned under Article 15.7.1(f). This catch-all provision closes the door on beryllium-aluminium alloys and beryllium-nickel alloys, preventing engineers from finding alternative beryllium-containing systems to deliver the exceptional stiffness-to-weight properties that drove the original restrictions.

Tungsten base alloys are prohibited inside the PU perimeter under 15.7.1(d), which means the general permission for tungsten alloys that applies outside the perimeter does not carry through. The distinction between tungsten base alloys and components that contain tungsten is important: the regulation does not ban tungsten outright inside the perimeter. It bans alloys where tungsten is the primary base material. Tungsten counterweights on crankshafts and tungsten in torsional damper elements are separately permitted as targeted exceptions because their functional purpose, concentrating mass in a defined location, is clearly separate from the general performance motivation that the ban is designed to prevent.

Alloys where the combined weight fraction of platinum, ruthenium, iridium, and rhenium exceeds 5% are prohibited under 15.7.1(c), targeting exotic high-temperature alloy systems that could be engineered for turbine and combustion components where elevated temperature performance is the dominant design criterion. The 5% threshold permits trace additions of these elements in conventional nickel superalloys while excluding compositions engineered specifically for their rare-metal content.

Nanomaterials and the Density Cap

Article 15.7.1(j) prohibits components inside the PU perimeter where at least one element of the material is a nanomaterial during production. This wording extends the prohibition to manufacturing routes that use nanomaterial processing as an intermediate step even when the finished component contains no detectable separate nanomaterial phase. The provision reflects both precautionary occupational health reasoning and concern about the long-term predictability of nanomaterial-enhanced structural materials in an environment combining high temperatures, vibration, and cyclic mechanical stress over a race weekend distance.

A separate density cap prohibits materials exceeding 18,400 kg/m3 inside the perimeter under 15.7.1(l). This threshold eliminates osmium, iridium in bulk form, and similar extreme-density elemental metals from structural or ballast roles within the PU boundary. For a full picture of where PU perimeter material rules sit within the complete Article 15 framework, the 2026 F1 Materials and Construction guide covers the permitted palette, prohibitions, and component-specific requirements across the entire car.

Component-Specific Requirements

The Iron-Based Core Components

Article 15.8 specifies materials at the individual component level for the internal combustion engine’s primary reciprocating and rotating parts. Pistons must be manufactured from iron-based alloys, with the regulations specifying approved designations including AMS 6487, 15CrDV6, 42CrMo4, and X38CrMoV5-3. These are all steel alloys, which might seem counterintuitive given the weight penalties compared to aluminium or titanium, but the thermal and mechanical demands on a piston operating at the combustion pressures and temperatures of a Formula 1 engine place them beyond what aluminium can reliably sustain at the bore dimensions and compression ratios the teams are running.

Piston pins must also be iron-based and manufactured as a single piece with no joining. Connecting rods are permitted in either iron-based or titanium-based alloys, again as single-piece components without welding, reflecting the cyclic fatigue loading that makes joined components a risk in this application. The crankshaft must be an iron-based alloy, a requirement driven by the combination of torsional stress, bending loads, and surface fatigue demands that make steel the consistently reliable choice despite its density. Camshafts are similarly restricted to iron-based alloys in single-piece construction per individual lobe.

Valves: The TiAl Exception

Valves represent one of the more technically interesting material provisions in Article 15.8 because they are explicitly permitted to use titanium aluminide (TiAl) intermetallic material, even though intermetallic alloys are generally prohibited inside the PU perimeter. This exception exists because TiAl offers a combination of low density and retention of stiffness and strength at the elevated temperatures that exhaust valves experience, which conventional alloys cannot match without a significant mass penalty.

Hollow exhaust valves are permitted, allowing teams to reduce reciprocating mass further by removing material from the valve stem and head interior. The material alternatives to TiAl for valves are alloys based on iron, nickel, cobalt, or titanium. Each of these alloy families covers a broad range of compositions with different performance characteristics at operating temperature, giving PU manufacturers meaningful room to differentiate their valve material strategies within the regulatory framework.

Exhaust and Turbine Housing Materials

Article 15.9 covers the pressure charging and exhaust systems that connect the internal combustion engine to the turbocharger. Exhaust components in direct contact with exhaust gas must be iron-based or nickel-based alloys. The Inconel family of nickel superalloys is specified by name for exhaust primary and secondary pipes, flanges, brackets, and the turbine housing, with the permitted grades limited to Inconel 625, 625 LCF, and 718. This restriction within the permitted nickel alloy family prevents use of higher-performance superalloy grades whose development cost and raw material cost would escalate expenditure in a component area where the FIA has chosen to contain the competitive arms race.

Static components in the pressurized and exhaust system that are not in direct contact with the exhaust gas or compressor airflow have a broader material palette, permitting iron-based alloys, aluminium alloys, or titanium alloys. The compressor housing is specifically permitted to use aluminium alloys containing up to 2.5% lithium, which is an exception to the general 1.0% lithium limit inside the PU perimeter and reflects the structural and thermal demands of the compressor inlet environment. The compressor wheel itself may be aluminium alloy up to 2.5% lithium or a titanium alloy, giving manufacturers the choice between the two material families depending on their design priorities for this highly stressed rotating component.

Energy Recovery and Electronic Systems

Casings and Structural Materials

Article 15.10 governs the materials inside the PU perimeter that relate to the energy recovery, energy storage, and electronic systems. Metallic casings for energy recovery systems and energy storage devices must be aluminium-based alloys, a requirement that combines adequate structural performance with the thermal conductivity needed to manage heat dissipation from these components. Electronic system casings, excluding energy recovery and storage housings, may be either polymeric materials or aluminium-based alloys, giving engineers more flexibility in packaging electronics within the weight and space constraints of the PU perimeter.

Soft Magnets and the Cobalt Constraint

Soft electromagnetic materials used inside the PU perimeter are explicitly released from several of the general 15.7.1 prohibitions, including the magnesium ban and the intermetallics ban, recognizing that the material requirements for high-performance electrical machine components differ fundamentally from structural requirements. However, cobalt content in soft electromagnetic materials is limited to 10% by weight under 15.10, reflecting both the cost of cobalt and concerns about the supply chain concentration of cobalt production.

An exception raises the cobalt limit to 49% where the cobalt used is both end-of-life recycled material and sourced from an ethical supply chain approved by the FIA. This provision is consistent with the broader sustainability direction built into the 2026 regulations, which also requires 100% non-fossil sustainable fuel. The higher cobalt content available through recycled supply incentivises the use of secondary materials in a component area where cobalt-iron alloys deliver superior magnetic performance compared to lower-cobalt alternatives.

Battery Cell Materials and the Energy Store

Energy store cells and permanent magnets inside the PU perimeter are also released from several of the general 15.7.1 prohibitions, specifically the bans on magnesium alloys, Metal Matrix Composites, intermetallics, and ceramics. This release is necessary because battery cell chemistry and permanent magnet materials for the MGU-K use material systems that would otherwise fall within the prohibited categories. Lithium-ion cell chemistry involves materials that do not fit neatly within the structural alloy framework the rest of the PU perimeter regulations address, and the FIA has appropriately separated these electrochemical and electromagnetic materials from the structural material rules.

Electronic components inside electrical units inside the PU perimeter face no material restriction at all under Article 15.10. The FIA’s rationale is that the components involved in circuit-level electronics are already governed by the standard supply requirements for the ECU and the homologation framework for power unit electronics, making additional material-level prescription redundant. Where the regulations do not reach, the cost and technical oversight of the standard supply and homologation systems provides an alternative form of control over what ends up inside these components.

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