Put two cartridges on a workbench. One says “thermal gel.” The other says “thermal putty.” They may behave differently—or, oddly enough, almost the same. These names are not standardized across the thermal interface material industry. A label is a clue, not a specification.
For a sound choice, compare cure behavior, rheology, gap range, assembly force, production, rework, and reliability.
The Names Overlap More Than Most People Expect
Thermal gel and thermal putty are both found within the wider liquid gap filler family. They replace insulating air between a heat-generating component and a heat sink, cold plate, metal housing, or heat spreader. Both can conform to rough surfaces and height variation while placing less stress on components than a stiff, heavily compressed pad.
In everyday engineering language, thermal putty usually means a thicker, strongly thixotropic, shape-holding material. It is commonly one-part and non-curing. Thermal gel often suggests a softer or more flowable dispensable material. Yet gel may be one-part and already stable, or it may be a two-part product that cures after mixing.
There is plenty of crossover. Parker Chomerics describes THERM-A-GAP GEL 75 as a one-part dispensable gap filler with a heavy, paste-like thermal putty consistency. That is one product wearing several perfectly normal industry names.
Laird’s liquid gap filler portfolio makes the same market overlap visible from another angle: it includes both one-part materials that remain uncured and two-part products that cure after application.
So, instead of forcing everything into two boxes, it is safer to compare three practical groups:
- One-part, shape-holding thermal putty
- One-part, softer or more flowable thermal gel
- Two-part cure-in-place thermal gel or gap filler
What Is Thermal Putty?
A one-part thermal putty is generally ready to dispense. It does not require an A/B mix or a secondary cure. Its paste-like, sometimes dough-like consistency helps it stay where it is placed before the enclosure is closed.
Putty suits irregular geometry and components with different heights. Imagine a row of little buildings: a VRAM chip is one height, an inductor is taller, and a controller sits lower. A preformed pad must compress across that uneven skyline. Putty can deform locally and fill the changing space.
Common uses include GPU memory and voltage regulators, telecom boards, server power sections, automotive controllers, LEDs, and industrial electronics with cast housings.
Shape retention does not mean the material is structural. Most putties still need screws, clips, or the enclosure to hold the parts together. They should not be treated as adhesives, environmental seals, or EMI shields unless the specific grade was designed and validated for those functions.
What Does “Thermal Gel” Mean?
This is where the language gets a little messy. Gel can describe two rather different production routes.
One-Part Pre-Cured or Non-Curing Gel
A single-component thermal gel is ready to use and needs no mixing. Some suppliers call these materials pre-cured because their useful structure already exists before dispensing. They remain soft and can often be removed for service.
Compared with a product sold as putty, a one-part gel may have easier flow and better wetting at a thinner bond line. That can help when the available assembly pressure is low. Still, this is a tendency, not a rule. Some commercial “gels” are thick enough to behave like putty.
Two-Part Cure-in-Place Gel
A post-curing thermal gel starts as two components. Metering equipment combines A and B, usually through a static mixer. The material is dispensed, then cures into a soft elastomer.
That cured form can improve positional stability. But production now has more moving pieces: mix ratio, air control, working time, mixer life, cure temperature, and cure time.
A cured gel may grip surfaces, but grip is not the same as qualified structural bonding. If the assembly needs an adhesive, specify a thermally conductive adhesive and test the joint accordingly.
Thermal Gel vs Thermal Putty: Side-by-Side Comparison
The table below describes common tendencies. A product datasheet and representative assembly trial always outrank the category label.
| Selection factor | Typical one-part putty | Typical one-part gel | Typical two-part curing gel |
| Supplied state | Ready to dispense | Ready to dispense | Separate A and B components |
| Cure behavior | Usually non-curing | Usually non-curing or pre-cured | Cures after mixing |
| Rheology | Stiffer, strong shape retention | Often softer or more flowable | Flows during application, then becomes a soft solid |
| Gap fit | Variable or larger uneven gaps, grade-specific | Thin-to-moderate variable gaps, grade-specific | Variable gaps where cured stability is useful |
| Assembly force | Usually low | Often very low | Low before cure; cured modulus depends on grade |
| Vertical stability | Depends on slump resistance | Depends strongly on formulation | Often improves after cure |
| Production process | One-part dispensing | One-part dispensing | Meter, mix, dispense, and cure |
| 作り直す | Often straightforward; apply fresh material | Often straightforward; apply fresh material | May require peeling and more residue cleanup |
| Main process risk | Underfill, overfill, slump, separation, equipment wear | Migration, flow drift, thin-area starvation | Ratio error, poor mixing, air, incomplete cure |
Notice what the table does not say. It does not declare one family more conductive, cheaper, or longer lasting in every application. Those claims need grade-level evidence.
Which Material Transfers Heat Better?
It is tempting to compare two W/m·K numbers and call the larger one the winner. Hmm, not so fast.
Heat must cross the whole interface. Performance depends on conductivity, bond-line thickness, wetting, contact resistance, and voids. A highly conductive material applied too thickly can create more resistance than a modest material forming a thin, complete interface.
Think of a winter coat. Expensive insulation does little if the coat does not cover your back. In the same way, headline conductivity cannot rescue a dry corner or a trapped air pocket.
Compare Thermal Impedance at the Real Bond Line
Ask how conductivity or thermal resistance was measured. Record thickness, pressure, temperature, surface condition, and specimen construction. “Typical” and “guaranteed minimum” are not the same thing.
ASTM D5470-17(2024) is widely referenced for steady-state thermal transmission measurements of relevant interface materials. It can support controlled comparisons. It does not reproduce every PCB, casting, clamping load, void, or environmental exposure in a finished device.
Confirm Performance in the Device
Test minimum and maximum production gaps, not only the nominal drawing. Measure component temperature under defined power and cooling conditions. Keep the fixture, sensor position, and assembly torque consistent.
The better material is the one that keeps the real component inside its thermal limit across tolerance. Sometimes that is gel. Sometimes putty. Occasionally both work, and production cost breaks the tie.
Mechanical Behavior Often Decides the Choice
Gap Variation and Component Stress
A shape-holding putty can bridge uneven components without one fixed pad thickness. A softer gel may wet a thinner interface more readily. Force still depends on contact area, gap, closing speed, stops, and rheology.
Board warp, component tolerance, housing flatness, and screw sequence can create a different gap at each corner. A material that works at 1 mm may squeeze away at the minimum or miss contact at the maximum.
Vertical Mounting, Slump, and Migration
The word “putty” sounds stable. The word “gel” sounds runny. Real life is not so tidy.
A one-part putty may slump when a tall bead gets hot. A good one-part gel may remain stable. A two-part gel can stabilize after cure but move beforehand if transported too soon.
Request vertical-stability evidence at the real thickness and temperature. Test the assembly in its shipping and operating orientation.
Pump-Out, Oil Bleed, and Aging
Thermal cycling and vibration add motion. A soft interface may shift, bleed oil, lose contact, or harden. Cured material can face cracks, adhesion changes, or internal voids.
No category name guarantees ten years of service. Review aged thermal impedance, appearance, mass loss where relevant, and device temperature after the environmental profile.
Production: One-Part Simplicity or Two-Part Stability?
One-part gel and putty avoid ratio and cure controls. Production still needs control over conditioning, feed pressure, shot volume, bead position, nozzle condition, and traceability.
Two-part gel adds meter-mix equipment. Control ratio checks, mixer replacement, purging, air, assembly timing, and cure. A partly cured mixer can change flow before blocking—one of those annoying failures that looks like a robot problem.
For more context on related names, the article about putty versus gap filler terminology explains why “gap filler” is the broader family.
Compare Total Process Cost
Price per kilogram is only one line. Also include:
- Deposit volume and waste
- Packaging and dispensing equipment
- Cycle and cure time
- Nozzle, mixer, pump, and seal replacement
- Inspection, cleanup, and rework labor
- Number of TIM grades or pad thicknesses kept in stock
- Field-failure risk
Putty may simplify a bill of materials by replacing several pad thicknesses. A curing gel may add equipment but reduce movement after assembly. A softer one-part gel may support a thin bond line and fast automation. The cheapest purchase can be the expensive process. Happens all the time.
Can Thermal Gel Replace Thermal Putty?
Possibly, but do not approve a name-to-name substitution. Compare the two actual grades.
Use this checklist:
- Confirm one-part or two-part construction and cure behavior.
- Test the full gap range and final bond-line thickness.
- Check wet-out at the available assembly force.
- Verify slump and stability in the actual orientation.
- Review thermal cycling, vibration, transport, and storage conditions.
- Confirm dielectric, chemical, coating, plastic, and seal compatibility.
- Check silicone, volatile, fogging, and cleanliness restrictions.
- Prove that production can dispense, inspect, and rework the substitute.
- Repeat the device-level thermal test.
Moving from a two-part curing gel to non-curing putty changes both production and final material state. A one-part gel-to-putty change may be smaller. Similar appearance is still not evidence of equivalence.
Be Careful Around Bare CPU and GPU Dies
Consumer forums often ask whether gap gel or putty can replace paste on a CPU or GPU die. Those thin, highly loaded interfaces normally use a qualified direct-die TIM. VRAM, VRM components, and coils often use thicker pad-replacement material.
Follow the OEM construction. If putty under nearby components is too thick, it may hold the cooler away from the die. That small mechanical error can send core temperature the wrong way, even when the putty itself conducts heat well.
Application Guide by Industry and Interface
| アプリケーション | What drives the choice | Useful starting direction |
| GPU VRAM, VRM, and mixed-height boards | Gap variation, cooler contact, rework | Shape-holding one-part putty or qualified one-part gel |
| Telecom radios and outdoor electronics | Vertical stability, cycling, automation, contamination | Grade-specific one-part material or curing system after testing |
| EV batteries and inverters | Large area, throughput, voids, vibration, dielectric needs | Automated one-part or two-part gap filler matched to the process |
| Servers and data-center hardware | Dense layouts, serviceability, thermal margin | Reworkable gel or putty validated at the real bond line |
| Optical modules, sensors, and relays | Siloxanes, fogging, residue, outgassing | Silicone-free thermal gel with a defined cleanliness test |
| LEDs and industrial controls | Cast surfaces, long operating time, orientation | Slump-resistant putty/gel or cured material based on geometry |
These are screening directions. A battery tray and a tiny optical transceiver may both contain “thermal gel,” yet need different chemistry and process controls.
Standards and Tests to Review
Standards control a method or provide a framework. They do not choose the product for you.
ASTM D5470 may support thermal comparison. IEC 60068 methods can inform temperature, humidity, vibration, and shock plans. ASTM E595 may apply to outgassing programs. UL 94 classifications may matter for certain material and device decisions.
For electrical insulation, review dielectric strength, volume resistivity, minimum thickness, creepage, clearance, edges, humidity, and aging. A brochure claim does not certify the complete assembly.
Use 一般的なTIM試験規格 as reference points, then add application-level testing. For sensitive optics, relays, sensors, or coated contacts, chemistry and contamination testing may matter as much as thermal performance.
What to Send a Supplier Before Choosing Gel or Putty
A useful supplier brief includes:
- Interface drawing and contact area
- Minimum, nominal, and maximum gap
- Heat source, power, and target temperature
- Heat sink or housing surface, assembly load, and mechanical stops
- Orientation, vibration, temperature, humidity, and service life
- Dielectric, flammability, regulatory, and contamination requirements
- Production rate, package size, and dispensing equipment
- Cure, rework, current material, and observed failure
If several options still look close, use 材料選定および試験サポート to build a small, controlled comparison. Two or three well-chosen candidates usually teach more than a pile of samples tested under vague conditions.
結論
Thermal gel and thermal putty overlap more than their names suggest. Putty often means a stiffer, shape-holding, one-part gap material. Gel may mean a softer one-part product or a two-part material that cures. But suppliers do not all draw the line in the same place.
Choose by behavior: cure state, rheology, gap range, bond line, assembly force, orientation, production method, rework, and aged interface performance. The best option is the one that keeps contact across real tolerance and real production. The label? Useful, sure. Just not enough.
よくある質問
Are Thermal Gel and Thermal Putty the Same Thing?
Sometimes they describe very similar one-part dispensable gap fillers. In other cases, gel means a softer material or a two-part curing product, while putty means a stiffer non-curing compound. Check cure, rheology, gap range, and process rather than relying on the name.
Is Thermal Gel More Flowable Than Thermal Putty?
Often, yes, but not always. Some one-part gels are heavy, paste-like materials that hold their shape much like putty. Use viscosity, thixotropy, slump, and dispensing data from the specific grade.
Does Thermal Gel Cure After Application?
It depends. One-part pre-cured or non-curing gels need no secondary cure. Two-part gels begin curing after A and B are mixed. Their ratio, working time, cure schedule, and final modulus must be controlled.
Can Thermal Gel Replace Thermal Putty?
It can if the actual gel meets the same interface, process, electrical, rework, and reliability requirements. Validate gap coverage, assembly force, orientation, bond-line thickness, thermal performance, and aging before approving the change.
Which Is Better for Large or Uneven Gaps?
A shape-holding putty is often a good starting point for tall or uneven gaps. A suitable gel or two-part gap filler may also work. The supplier’s validated gap range and assembly trial matter more than the category name.
Which Material Is Easier to Remove and Rework?
One-part putties and gels are often easier to wipe or scrape away than cured two-part materials. Apply fresh material after opening the interface. Do not reuse a removed compound that has changed shape or picked up dust and debris.
Can Thermal Gel or Putty Leak, Slump, or Dry Out?
Either can move or age if the formulation, gap, temperature, orientation, or assembly is unsuitable. Review grade-specific stability data and test the complete device after thermal cycling, vibration, storage, and relevant environmental exposure.
Are Thermal Gel and Thermal Putty Electrically Insulating?
Many grades are designed to be electrically insulating, but not every product is. Confirm dielectric data and validate the complete insulation system, including minimum thickness, edges, creepage, clearance, humidity, and aging.
Can Thermal Gel or Putty Be Used Directly on a CPU or GPU Die?
Do not assume so. Direct-die interfaces usually need a TIM qualified for a thin bond line and the specific clamping design. Putty and gap gels are more commonly used on height-varying VRAM, VRM, coils, and nearby components.
How Should Thermal Performance Be Compared Before Selection?
Compare thermal impedance or resistance at representative thickness and pressure, then test component temperature in the real assembly. Use the same power, ambient condition, cooling setup, sensor position, assembly force, and steady-state rule for each candidate.
