XJ is loud - thin sheetmetal, rear cargo echo, road noise. Dynamat Xtreme, Kilmat, or Noico butyl/foil mats reduce noise by 5-10 dB. Apply to floor, doors, roof, cargo wheel wells.
XJ sound deadening priorities (most to least impact):
1) Floor pan (under carpet): biggest contributor to road noise. Apply 60-80 sq ft of Dynamat Xtreme or Kilmat 80 mil to the entire floor pan from firewall to rear cargo. Cover at least 25% surface area, 60% is excellent.
2) Front doors: tin-can sound. Apply to inner door skin (behind speaker hole). 15-20 sq ft each door. Closes with a thump instead of a clang.
3) Rear cargo wheel wells: amplifier of tire noise. 8-15 sq ft each side.
4) Roof: under the headliner (great opportunity if doing the headliner anyway). 25-35 sq ft. Reduces rain noise and metal flex.
5) Trunk floor under spare tire well: 10 sq ft.
Total for a full XJ: 100-150 sq ft. Costs ~$200-300 for Kilmat (budget), $500-700 for Dynamat Xtreme (premium). Performance difference is small — Kilmat has a slight smell when warm but otherwise comparable.
Application: clean metal with isopropyl alcohol, peel backing, apply firmly with roller (wallpaper roller works). Don't cover drain holes! Don't cover the upper firewall or hood (heat).
Layer on top of butyl with closed-cell foam (CCF) like Noico RED for higher frequency dampening. Mass-loaded vinyl (MLV) blocks transmission but is heavy and unnecessary on most XJ builds.
| Part | Vendor | Est. price |
|---|---|---|
| Kilmat 80 mil 50 sq ft | Kilmat | ~$90 |
| Dynamat Xtreme 36 sq ft Bulk Pack | Dynamat | ~$240 |
| Noico RED 170 mil closed-cell foam 35 sq ft | Noico | ~$70 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.