Two cases. High temperature: a premium hot-face layer (ceramic/silica/microporous) rated for the duty, backed by cheaper stone wool doing the bulk resistance where it's now cool enough — standard furnace and exhaust practice. Large thickness: above ~100 mm single-layer, two staggered layers kill the through-joint convection paths a single thick layer leaves. Design note: interface temperature between layers must stay below the outer material's limit — computed, not guessed (the calculator's design mode solves it).
Compute your own case: free heat-loss calculator · materials library: 12 datasheets · related: What is CUI (corrosion under insulation)? · What is economic thickness of insulation? · R-value vs k-value (λ) — what's the difference? · What insulation works at 600 °C?
