diff --git a/deploy/busbar-designer.service b/deploy/busbar-designer.service
index 03d0b89..65bc3e0 100644
--- a/deploy/busbar-designer.service
+++ b/deploy/busbar-designer.service
@@ -23,6 +23,10 @@ Environment=HOST=0.0.0.0
 Environment=PORT=5000
 Environment=FLASK_DEBUG=0
 Environment=PATH=/opt/busbar-designer/.venv/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+; Use OpenSCAD nightly (extracted AppImage) for the Manifold backend.
+; Falls back to system "openscad" (CGAL) if this binary is missing.
+Environment=OPENSCAD_BIN=/usr/local/bin/openscad-nightly
+Environment=OPENSCAD_BACKEND=Manifold
 ; HOME points inside the project so ezdxf / matplotlib / build123d can write
 ; their config + cache while ProtectHome=true still hides the real /home.
 Environment=HOME=/opt/busbar-designer/data
diff --git a/holder.py b/holder.py
index 80ee1f1..8e518ee 100644
--- a/holder.py
+++ b/holder.py
@@ -28,6 +28,8 @@ from typing import Any
 APP_DIR = Path(__file__).resolve().parent
 SCAD_FILE = APP_DIR / "scad" / "hex_cell.scad"
 OPENSCAD_BIN = os.environ.get("OPENSCAD_BIN", "openscad")
+# Empty string disables; default Manifold gives ~10-50x speedup on OpenSCAD 2024+
+OPENSCAD_BACKEND = os.environ.get("OPENSCAD_BACKEND", "Manifold")
 RENDER_TIMEOUT = int(os.environ.get("OPENSCAD_TIMEOUT", "300"))
 
 
@@ -210,6 +212,8 @@ def render_stl(params: dict) -> bytes:
     with tempfile.TemporaryDirectory() as tmp:
         out = Path(tmp) / "out.stl"
         cmd = [OPENSCAD_BIN, "-o", str(out)]
+        if OPENSCAD_BACKEND:
+            cmd += ["--backend", OPENSCAD_BACKEND]
         for k, v in clean.items():
             cmd += ["-D", f"{k}={_to_scad_literal(v)}"]
         cmd.append(str(SCAD_FILE))