THERMAL STRAPS
WHAT ARE THERMAL STRAPS?
Thermal straps are flexible conductive links designed to transfer heat efficiently while mechanically isolating vibration between connected components. Also referred to as flexible thermal links, thermal braids, thermal shunts, or heat straps, they provide passive heat transfer using high-conductivity materials such as OFHC copper, aluminum, pyrolytic graphite sheets, graphite fiber, and graphene composite foils.
A typical thermal strap consist of two or more end fittings (terminals or lugs) used to attach the strap to the heat source and sink interfaces, joined by the flexible, high-conductivity material. The flexible element enables efficient heat flow between a source and sink while minimizing the transmission of vibration, shock, and thermally induced mechanical stress.
WHY USE THERMAL STRAPS FOR VIBRATION-ISOLATED HEAT TRANSFER?
Thermal straps are widely used in aerospace, cryogenic systems, quantum computing, photonics, semiconductor equipment, synchrotron beamlines, and scientific instrumentation where both waste heat removal and vibration isolation are critical, as they offer a unique combination of benefits that other active and passive heat transfer technologies lack.
Unlike rigid, passive cooling products like bus bars, heat pipes, or heat fins, or active devices such as or thermal switches, TEC's, or various liquid cooling solutions, thermal straps:
- Provide mechanical decoupling between thermally connected components
- Can accommodate a wide range of motion or deflection (critical in sample holders and deployable structures)
- Reduce transmission of vibration from cryocoolers and other dynamic systems
- Accommodate differential thermal expansion and contraction
- Operate without working fluids, electronics, or moving parts (that can put expensive systems at risk or perform poorly in zero gravity)
- Offer predictable, reliable performance across a wide temperature range
As a result, thermal straps are widely used for numerous applications in the aerospace, cryogenics, photonics, semiconductor, synchrotron, and quantum computing industries:
- Cryocoolers, cryostats, and dilution refrigerators
- Star trackers and precision optical instruments
- Electronics enclosures and detector assemblies
- Photonics and laser systems
- Spacecraft and satellite thermal control systems
Thermal straps are often paired with or integrated into other thermal management systems. For example, they may be used alongside and even be directly clamped to heat pipes to provide additional vibration attenuation while maintaining high heat transport capability. In certain designs, straps can be directly integrated into cold plates, vapor chambers, or other thermal hardware to optimize interface performance and simplify assembly.
(For a technical comparison, see our resource: Thermal Straps vs Heat Pipes and Vapor Chambers).
THERMAL STRAP MATERIALS AND TYPES
METALLIC FOIL AND BRAID/CABLE THERMAL STRAPS
Thermal straps fabricated from copper braid, copper cable, and stacked metallic foils (copper or aluminum) have been used for decades in various thermal management systems. These metallic configurations are durable, versatile, and capable of operating across an exceptionally wide temperature range — from millikelvin environments in dilution refrigeration systems to elevated temperatures exceeding 800K in propulsion-adjacent aerospace applications.
In many terrestrial, laboratory, and spaceflight systems where extreme mass reduction is not the primary constraint, metallic thermal straps provide an effective and economical solution.
COPPER CABLE THERMAL STRAPS (CuTS®)
Copper thermal straps made from braided wires (flat braid, rope, cables) are often soldered, brazed, or welded. However, these assembly processes are not ideal for most aerospace, semiconductor, or cryogenic engineering applications. This is because they result in exponentially higher thermal resistance losses and significantly increased stiffness (as the heat from these processes wicks up the cables). Increased stiffness can transfer vibrations and damage equipment. To avoid these negative drawbacks, TAI manufactures our straps via a swage ("cold press") process. This heat-free assembly method offers unmatched efficiency and preserves the flexibility of the conductive materials used in a thermal strap. We also only use OFHC copper (C101), as more than half of our strap customers have cryogenic applications, and OFHC copper offers superior performance over ETP copper below 77K.
When considering flexibility, durability, and performance, a copper cabled strap is the preferred, and most frequently used, in all industries and applications. Further, TAI's exclusive OFHC UltraFlex™ I and II cabling (used on all standard and custom CuTS®), offers customers the optimal combination of flexibility and thermal performance. CuTS® offer flexibility on all axes, and can handle exponentially greater loads and life cycle flexing than any other strap or material type.
COPPER CABLE THERMAL STRAP DESIGN TRADEOFFS AND CONSIDERATIONS
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Mass: Copper has a higher density than other conductive strap materials, and in extremely mass-sensitive applications, a graphite strap may be your best option. However, TAI can substitute AL 6061 for the end fittings in many of our CuTS® designs, thereby reducing the total mass of a strap by 40-60% on average. It is important to note that while aluminum is less dense than copper, aluminum foil straps are not always an ideal alternative (where mass is a concern). Aluminum offers a fraction of the conductivity of copper, and stacked aluminum and copper foil straps must be designed into longer C and U-shaped installation configurations (with at least a 180 degree curve), in order to provide any flexibility on all 3 axes, and in full S-shapes to achieve a wide range of motion (i.e. typically greater than 1mm), on the lateral/transverse axis. As a result of this longer length, they must be made with more sheets to match the thermal performance of a copper cabled strap, thereby increasing the mass.
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Stiffness at shorter lengths - copper rope straps—even those made by TAI—can be stiff if multiple rows are incorporated into the design AND the cable length is less than 1.0 inch (25.4mm). At these shorter lengths, cables continue to offer superior flexibility over stacked metallic foils, but the increased stiffness of the assembly is noticeable.
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Cross-sectional area: a cable (or braid), by its very nature, is not as densely-packaged as a stack of metallic sheets. As a result, cabled straps may not meet your thermal conductance requirement in certain volume-restricted applications.
COPPER & ALUMINUM FOIL THERMAL STRAPS (CuFS®, AlTS)
Volume-restricted applications (requiring high thermal performance), may benefit from a stacked metallic foil configuration. However, there are a number of trade offs to consider:
METALLIC FOIL THERMAL STRAP DESIGN TRADEOFFS AND CONSIDERATIONS
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Stiffness: All metallic foil straps are inherently stiffer than equivalent cable configurations. To introduce flexibility — particularly in compression and transverse directions — foil straps are often installed in U-shaped or S-shaped geometries. These configurations however, increase the over strap length (thereby increasing mass and the amount of conductive material required to meet your performance target), and can increase the required volume for a strap.
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Assembly Methods - conventional assembly methods (brazing/soldering/welding), dramatically increase stiffness and resistance losses at the joints (which is why swaged foil straps are preferred).
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Price - metallic foil straps typically cost 2-5x more than copper cabled straps. Not only are the materials more expensive, but the assembly process is more complex and involves additional steps (thus, the higher price).
In many cases, foil straps are not the ideal solution. However, there are specific applications and environments in which they may offer benefits over a graphite or copper rope strap. TAI's engineers work directly with our customers to evaluate these variables and recommend the most appropriate strap configuration.
GRAPHITE AND GRAPHENE SHEET & FIBER THERMAL STRAPS
Pictured: Standard Model G6 and X6 Graphite Fiber, Graphene Composite, and PGS Thermal Straps (PyroFlex / PGL) manufactured by TAI for satellites and cubesats.
There are multiple carbon-based thermal strap solutions to consider. Initially, flexible graphite thermal links were used only for spaceflight applications operating between 230 - 400K. However, high conductivity graphite materials (like pyrolytic graphite film, graphene layered foils, and graphite fiber), also offer a unique set of benefits over a wide range of operational and environmental conditions, and they are now incorporated into terrestrial and spaceflight cryogenic applications.
Each carbon-based thermal strap product offers a combination of mechanical, thermal performance, and financial costs to consider. It is important to note that graphite fiber and sheet should not to be confused with rigid Annealed Pyrolytic Graphite (APG), which is not flexible enough to be used as a true thermal strap, or graphene layered foils, which fracture with movement.
HOW HEAT FLOWS IN GRAPHITE THERMAL STRAPS
One of the most significant differences between graphite and metallic-based thermal straps is how heat is transferred through the materials, and what can be considered the "bottleneck." In graphite straps, the heat transfers in-plane with the graphite sheets or fiber bundles. As graphite offers orders of magnitude greater conductivity than copper or aluminum at warmer temperature ranges, the fitting size or "footprint" is largely irrelevant (plays little part in the overall performance). Instead, the primary purpose of the fitting is simply to act as a bracket that contains the graphite and attaches it to the interfaces.
As a result, the total length of the graphite material will significantly impact the thermal conductance of the assembly, as will (to a lesser extent), the end fitting design and distance from the edge of the graphite sheet stack or fiber bundles to the heat source and sink interfaces. This is why, when possible, allowing the graphite to make direct contact with the interfaces (the graphite attaches perpendicular to the interface, using L-shaped fittings), allows for a more efficient strap that minimizes thermal resistance losses.
This differs from copper and aluminum thermal straps, in which larger fittings can increase the conductance of the strap, and the "bottleneck" is the length of the flexible rope/braid/sheet material (given it's cross section relative to that of the solid fittings). Because of this, assuming the mass requirement is not exceeded, metallic straps can be made with longer fittings and a shorter flexible portion length (rope length), and in some cases, this approach can lead to a copper cable thermal strap with similar or even superior thermal performance to a graphite sheet or fiber thermal strap.
Pictured (top right): PGS Thermal Strap mounted to thermal conductance test fixture in TAI vacuum chamber #1.
GRAPHITE FIBER THERMAL STRAPS (GFTS®)
Graphite Fiber Thermal Straps (GFTS®) are constructed from GraFlex™, a bundled graphite fiber “tow” (rope) architecture engineered for high in-plane thermal conductivity (up to approximately 810 W/(m·K), material dependent).
Unlike copper cable or carbon sheet or film-based straps, fiber-based assemblies provide a balance of:
- High conductance-to-mass ratio
- Multi-axis flexibility (though stiffer than graphite sheets, they do not require a full 90 or 180 degree curve to offer lateral flexibility)
- Shape retention for complex routing geometries
Because the bundled fiber structure maintains dimensional stability, GFTS® assemblies can be assembled in their installed configurations and routed through constrained envelopes without sagging or settling into the path of least resistance. This can simplify integration in cryogenic, aerospace, and optical systems, while still allowing for superior vibration attenuation.
Pictured (above): Graphite Fiber Thermal Strap assembly used in the Phased Antenna Array Systems on NASA's ORION.
GRAPHITE FIBER THERMAL STRAP DESIGN TRADEOFFS AND CONSIDERATIONS
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GFTS® products—while more robust than graphite and graphene sheet/foil straps—are delicate, and more fragile than metallic straps.
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Fiber-based strap assemblies provide a fraction of the performance of their foil/film-based counterparts.
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GFTS® assemblies, like metallic foil straps, need to be designed and assembled into their installed configuration/shape, and do not offer an extensive range of motion on all axes (like a copper cabled strap).
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While they offer 3 axes of flexibility/deflection, GFTS® assemblies are best-suited to applications requiring less than 25mm of deflection on each axis, and are stiffer on the vertical and compression axes than a PGF-based strap.
PGS & GRAPHENE THERMAL STRAPS (PyroFlex™ & GTL™)
Pyrolytic graphite sheet and film (PGS / PGF), and engineered graphene-layered foil straps represent the highest in-plane thermal conductivity options available for flexible thermal links at temperatures above 80K.
At room temperature (300K), high-quality pyrolytic graphite can exhibit in-plane thermal conductivities of 1,000–1,800 W/(m·K), depending on grade and processing. This directional conductivity far exceeds that of copper or aluminum on a mass basis (at warmer operating temperatures) and makes these materials particularly attractive in mass- and volume-constrained systems, or those with particularly high conductance requirements.
TAI's PyroFlex™ Graphite Sheet Straps (previously referred to as PGL®) offer the highest thermal performance of any carbon-based strap at cryogenic operating temperatures (with performance peaking at 150K). They are an effective replacement for aluminum foil straps down to operating temperatures as low as 65K (and provide equivalent performance—at a lower mass—to OFHC copper thermal straps between 70 and 80K).
Pictured: X6 PGS Thermal Strap (PyroFlex®) without the mylar sleeve.
GRAPHITE & GRAPHENE SHEET THERMAL STRAP DESIGN TRADEOFFS AND CONSIDERATIONS
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All stacked pyrolytic graphite and graphene foils/sheets/films are fragile. These can be damaged if flexed on the lateral axis (when not designed for this type of deflection), or if improperly handled or used. Carbon-based sheet thermal straps, like metallic foil straps, must be installed in S-shapes, or curved 180° (or near 180°) arcs (C or U-shapes), in order to provide lateral deflection / coplanar to the sheet material (though a 90° bend / "L-shaped" graphite sheet strap can usually achieve a 1mm lateral deflection).
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Carbon-based straps are not ideal at operating temperatures below ~60K, unless the goal is to use them as a flexible thermal switch. Graphite thermal links can be used in addition to copper thermal straps, to reduce cool-down times of cryocoolers and cryostats, and then effectively cease heat transmission between 10-40K, depending on the material.
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Graphite/Graphene Sheet/Foil straps are expensive. Though Graphite Fiber Strap products now sell for the same price as competing metallic foil straps, graphite sheet-based products have moderately higher material and assembly costs.
HOW TO SELECT THE RIGHT THERMAL STRAP FOR YOUR APPLICATION
Pictured: thermal conductivity graph of commonly used flexible thermal strap materials.
Flexible thermal links or straps have existed in various forms for decades, ranging from simple copper braid shunts used in automotive, LED, and electronics applications to the highly engineered, precision-manufactured flexible thermal links used today in spacecraft, defense systems, lightsource & beamline systems, and advanced cryogenic platforms.
No single thermal strap or material is ideal for all applications. Thus, selecting the right thermal strap—and the appropriate level of performance and manufacturing quality—depends on application requirements, operating temperature, mass constraints, and reliability expectations:
| THERMAL CONSIDERATIONS | MECHANICAL CONSIDERATIONS | SYSTEM & PROGRAM CONSTRAINTS |
| Required Thermal Conductance | Flexibility, Stiffness and Range of Motion | Mass Limits |
| Operating Temperature Range | Vibration Isolation Requirements | Volume Restrictions |
| Temperature Gradients and Stability Requirements | Load-Bearing Demands | CTE Compatibility |
| Material Conductivity at Target Temperature | Life-cycle Bending or Dynamic Motion | Budget, Production Volume |
Which thermal strap solution you choose most frequently starts with your operating temperature and the conductance requirement. Once those parameters are established, you must weigh the other requirements to determine which conductive, flexible material is best suited to your operational environment and the mechanical requirements of your system.
CRYOGENIC APPLICATIONS
(mK - 100K)
Cryogenic applications are ideal for high purity metallic thermal straps (OFHC copper and "5N" pure copper or aluminum foil), as the thermal conductivity of these materials spikes below 77K, whereas the conductivity of carbon-based materials drops rapidly below 150K (-123C). OFHC copper cable thermal straps are typically the best solution in this range, because they offer superior flexibility at a small fraction of the cost of 5N pure cu and al foil straps (and they can be vacuum annealed to dramatically increase performance at cryogenic temperatures if needed).
COMMON APPLICATIONS
• Dilution Refrigerators
• Cryocoolers
• Cold Boxes
• Cryo Modules
• Beamlines
• Superconducting Magnets & Other Components
• Detectors and Sensors
• Cryostats
• Focal Planes
Pictured: P5-506R and P5-502 Copper Cable Thermal Straps mounted in Cryostat.
"COLD" APPLICATIONS
(100K - 250K)
Applications operating in this range are commonly found in cold laboratory equipment and satellites. Across this temperature range, which thermal strap solution you choose will depend on a combination of factors ranging from the conductance requirement, to deflection/range of motion on each axis, mass limits, and your budget. Across this range, high conductivity graphite thermal straps begin to outperform metallic straps. However, their cost may be the deciding factor (graphite straps typically cost 2-5x more than metallic straps due to the materials and labor required).
COMMON APPLICATIONS
• Optical Systems
• Star Trackers
• Telescopes
• Electronics Boxes
• Detectors and Sensors
• Microwave Antennas
• Cryocoolers
• Radiators
• Laser Pointing Systems
Pictured: ESA satellite Graphite Fiber Thermal Straps mounted in vibe test fixture.
"WARM" APPLICATIONS
(250K - 400K+)
Like colder applications, "warm" operating temperatures (commonly found in aerospace & defense applications, electronics, and various photonics and optics systems), are ideal for both copper and graphite-based thermal strap products. Selecting the optimal thermal strap solution will again depend on a combination of factors ranging from the conductance requirement, to deflection/range of motion on each axis, mass limits, and your budget. Which solution you ultimately use will likely come down to balancing requirements and your budget.
COMMON APPLICATIONS
• Optical Systems
• Star Trackers
• Satellites and Cubesats
• Electronics Boxes
• Rockets
• Microwave Antennas
• Battery Cooling
• Medical Instruments
• Heat Pipe Connections
Pictured (above): PGS Thermal Strap mounted in Hyperspectral Thermal Imaging System.
CUSTOM THERMAL STRAP DESIGN AND ENGINEERING SUPPORT
TAI designs and manufactures standard model and fully custom thermal straps engineered to meet precise thermal, mechanical, and environmental requirements for any application. Our engineering team provides complimentary pre-order design assistance to help optimize strap geometry, materials, and interface configurations, taking into account important considerations such as installation sequence and tool access, to best position your program for success.
To begin your design inquiry:
- Download our thermal strap catalogs
- Complete our design questionnaire
- Provide CAD (STP files) detailing envelope constraints and the available interfaces
Our team will work with you to develop a solution tailored to your application, performance requirements, and budget, and we are always happy to provide guidance at no charge, as early on in the process as possible (before elements in your system become fixed and thermal solutions become limited).
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THERMAL STRAP FAQ
TAI's THERMAL STRAP HERITAGE
Our copper and graphite thermal strap design, test, and manufacturing heritage spans three decades. It began with our own Scott Willen and Richard Jetley, who developed the first Graphite Fiber Straps (GFTS®), in SBIR Ph I and II contracts with the USAF in 1996 (this research was later published in Cryocoolers 11). GFTS® products gained popularity in 2011 - 2013 as several dozen assemblies, designed and manufactured by TAI Quality Manager, Trevor Sperry, were used to cool the phased antenna arrays and data acquisition systems on the ORION spacecraft, and compressors on JAXA's Astro-H satellite.
Since 2015, GFTS® have played vital roles in notable programs such as Boeing's CST-100 Starliner, NASA's IXPE and GRACE-FO satellites, ESA's Solar Orbiter, DLR’s EnMAP, and several other spaceflight missions (in addition to ground-based applications in the medical and cryogenic engineering industries).
Our Copper Cabled Strap (CuTS®) heritage began in 2004, with our first-generation solderless copper braided straps (offered until 2014). TAI was the first and only supplier to offer a fully customizable standard product line and catalogs, both created by our Director of Business Development, Tyler Link, in 2013. Two years later, TAI developed OFHC UltraFlex cabling, optimized end fitting design, and improved swage & final machining methods. In 2017, this new generation of straps was studied extensively by Fermi National Lab and other universities and laboratories (research was later published in volume 86 of the Journal Cryogenics, and co-authored by TAI's Tyler Link and Jamie Deal).
Work with Pyrolytic Graphite Film-based straps began in 2013, culminating in the X-Series® Strap; the world's first and only graphite and graphene sheet thermal strap standard product line. X-Series® PGF-based thermal links (PyroFlex™) were then space-qualified by NASA JPL in 2018. They advanced to TRL 8 with spaceflight qualification testing performed by Airbus and the DLR, on the Merlin program, and then TRL 9 with multiple space flights on cubesats, nanosats, and other commercial crew and cargo vehicles since 2023. PyroFlex™ straps now play vital roles in space flight programs for aerospace companies across the US, Europe, and Asia, and at NASA, JAXA, and ESA.