A hot face may provide mechanical protection, control gas or vapor movement, influence heat transfer, or make a damaged surface easier to replace. These functions are related, but they are not interchangeable.
C/C hot face
A carbon-fiber-reinforced carbon sheet protects the insulation from handling damage and gas erosion. C/C is a carbon matrix composite—not an epoxy carbon-fiber laminate.
What changes with the choice
Its performance depends on thickness, weave, density, attachments and edge details. A sheet is not automatically a sealed vapor barrier.
Ask the supplier
Where does damage start: loading, gas jets, edges or fasteners? How will this face be removed and replaced?
Ipsen · Graphite felt and board in vacuum furnaces · Schunk · Insulation protection and microperforation
Graphite foil
Flexible graphite can serve as a liner or diffusion barrier. SGL describes its use to limit unwanted convection and protect insulation from process vapors.
What changes with the choice
Seams, holes and damage determine the installed barrier. “Reflective” alone does not establish a heat-loss improvement; compare the complete stack under the same conditions.
Ask the supplier
Is the priority a vapor barrier, a replaceable skin, a thermal effect—or all three? What are the foil grade, thickness and joint details?
C/C + graphite foil
C/C and graphite foil can be supplied as a composite. SGL’s Heatshield is one documented commercial example intended to protect furnace parts and insulation.
What changes with the choice
A bonded composite introduces an interface. Orientation, bend radius, bonding and thermal cycling belong in the selection—not just the names of its two materials.
Ask the supplier
Is this a laminate, a coating or separate layers? What are its assembly limits and repair method?
Perforated foil
Schunk lists microperforation as a way to prevent bubble formation in its graphite foil insulation protection.
What changes with the choice
Openings also change barrier continuity. The appropriate pattern depends on the stack and pressure cycle; more holes is not a general improvement.
Ask the supplier
What trapped-gas path is being relieved? What hole size and open area were tested, and under which evacuation and backfill rates?
Graphite edge coating
Schunk offers a graphite coating for protection of hard felt against gas erosion. That establishes a use for a specified coating on a specified substrate.
What changes with the choice
This does not qualify any graphite paint on soft felt. Binder, cure, adhesion and contamination must fit the operating environment. A coated edge is not necessarily gas-tight.
Ask the supplier
Is the supplier approving this felt, this edge treatment and this cure? What outgassing and repeated-cycle data are available?
Schunk · Graphite coating powder · SGL Carbon · SIGRATHERM rigid felt
Moly face + carbon backing
A metal hot face over carbon insulation is a distinct design question. Evaluate the metal, backing, seams and contact details as one assembly.
What changes with the choice
A molybdenum face does not make the underlying carbon disappear or establish a carbon-free process. Thermal movement, chemical compatibility and the complete gas path need review.
Ask the supplier
What problem is the metal face solving? Obtain the vendor’s exact stack, service history and compatibility evidence before treating it as an alternative.
For a trial, hold insulation thickness, density, geometry and cycle constant where possible. Record pump-down, holding power, ramp and cooling behavior, surface condition and maintenance after repeated cycles.
Sources & reading notes
- Ipsen · Graphite felt and board in vacuum furnaces
Craig Moller, Chief Engineer; manufacturer application discussion, date not stated.
- Schunk · Insulation protection and microperforation
Manufacturer application claims; date not stated.
- SGL Carbon · SIGRAFLEX liners and diffusion barriers
Manufacturer application overview; date not stated.
- SGL Carbon · SIGRABOND Heatshield
July 2021; C/C–graphite foil composite data sheet.
- Schunk · Graphite coating powder
Manufacturer application claim for hard felt; date not stated.
- Plansee · Molybdenum material definitions
Established material descriptions; revision date not stated.
Source check: October 1, 2026. Vendor claims are attributed. Questions and selection frameworks are HeatTreat.tech editorial analysis, not a qualified furnace design.