How does it differ from soft felt?

In stiffness. Rigid felt is consolidated, holds its shape, machines, and installs as a panel; soft felt conforms in layers to irregular geometry. They are usually used together: rigid panels as the wall, soft felt to close joints and penetrations.

Can rigid felt be machined?

Yes. It is cut and machined into discs, steps, recesses, and holes for element feedthroughs and fasteners. That is one of the reasons to prefer it where the zone demands a defined geometry.

How are joints between panels designed?

By accounting for contraction of the assembly during the cycle. Overlaps or soft-felt fillers are used at the joins so that the joint does not become a direct heat path when the assembly moves.

Which panel density is appropriate?

It depends on the balance between insulation and stiffness the zone requires. Higher densities give more strength and a more closed face; lower ones insulate with less mass. Values are compared on the material datasheet.

Rigid carbon/graphite felt liners and panels

Thermal applications

Furnace rigid felt liners

Carbon/graphite rigid felt liners, plates, and blocks for structural insulation in heat-treatment and vacuum furnaces.

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Rigid structural insulation

Also known as: Rigid carbon felt · Graphite insulation panels · Rigid felt board · Self-supporting furnace liners

Rigid felt panels and liners for insulation with structural support in high-temperature chambers.

[ Technical summary ]

Rigid felt is a carbon-fibre insulation consolidated with a carbonized binder, which gives it enough stiffness to be self-supporting and to be machined into panels, discs, and liners. Compared with soft felt, it holds shape and assembly clearances without continuous fastening, and presents a more closed face that reduces fibre shedding into the chamber. It is used as the primary insulation in vacuum and controlled-atmosphere furnaces.

Rigid felt liners and panels provide shape-stable insulation in heat-treatment furnaces and vacuum chambers. They are used as walls, roofs, disks, and low-conductivity structural elements.

They are often combined with soft felt: the rigid grade provides support and geometry; the soft grade fills gaps and improves the chamber’s thermal seal.

[ Problem it solves ]

Insulate large surfaces with a material that keeps its shape and assembly clearances, avoiding the compaction and open joints that appear when flexible insulation works without support.

Processes

Structural insulation of furnace chambers
Self-supporting liners and panels
Die-cut or machined disks and parts

Operating conditions

Vacuum and controlled atmosphere

When it is suitable

The insulation must be self-supporting or form the hot-zone wall
Fibre shedding toward the load has to be reduced
The zone has a large area and regular geometry
Installation uses panels replaceable section by section

When it may not be suitable

The process runs in air at high temperature without a protective atmosphere
The zone has irregular voids that call for a flexible material
The panel will take impact or direct mechanical load

Process challenges

Heat losses in large-area zones
Need for shape-stable insulation
Thermal shock during startups and shutdowns
Panel installation with controlled clearances

Advantages

Greater stiffness and dimensional stability than soft felt
Low thermal conductivity in vacuum
Machinable plates, blocks, and geometries
Combinable with soft felt liners

Limitations

Oxidation in air at high temperature
Less flexible for irregular voids (complement with soft felt)
Gasket and fastening design must account for shrinkage

[ Critical selection variables ]

These variables define the grade and the geometry. Actual values are confirmed against the grade datasheet.

Operating temperatureDecisive
Atmosphere (air, inert, vacuum)Decisive
Thickness and number of layersDecisive
Felt densityDecisive
Geometry and tolerancesRelevant
Fastening system and jointsRelevant
Required purity and allowable contaminationRelevant

[ Required material properties ]

Properties that guide selection. Numerical values come from each grade's datasheet.

Critical properties

Thermal conductivity
Purity
Thermal stability
Dimensional stability

Secondary properties

Bulk density
Machinability

[ Related ]

[ Frequently asked questions ]

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Technical content reviewed by ESGRAF — Last reviewed: September 8, 2026

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