diff --git a/Detectors/Upgrades/ALICE3/TRK/base/include/TRKBase/TRKBaseParam.h b/Detectors/Upgrades/ALICE3/TRK/base/include/TRKBase/TRKBaseParam.h
index d5e11313c0f0c..79588c1130c2b 100644
--- a/Detectors/Upgrades/ALICE3/TRK/base/include/TRKBase/TRKBaseParam.h
+++ b/Detectors/Upgrades/ALICE3/TRK/base/include/TRKBase/TRKBaseParam.h
@@ -34,6 +34,7 @@ enum eLayout {
 enum eVDLayout {
   kIRIS4 = 0,
   kIRISFullCyl,
+  kIRISFullCyl3InclinedWalls,
   kIRIS5,
   kIRIS4a,
 };
diff --git a/Detectors/Upgrades/ALICE3/TRK/simulation/include/TRKSimulation/VDGeometryBuilder.h b/Detectors/Upgrades/ALICE3/TRK/simulation/include/TRKSimulation/VDGeometryBuilder.h
index c337ddb102147..77b45c97cba84 100644
--- a/Detectors/Upgrades/ALICE3/TRK/simulation/include/TRKSimulation/VDGeometryBuilder.h
+++ b/Detectors/Upgrades/ALICE3/TRK/simulation/include/TRKSimulation/VDGeometryBuilder.h
@@ -25,6 +25,7 @@ namespace o2::trk
 // and then places/rotates the petal once into the mother volume.
 
 void createIRISGeometryFullCyl(TGeoVolume* motherVolume);          // Full-cylinder IRIS geometry (no petals, no gaps, no side walls)
+void createIRISGeometry3InclinedWalls(TGeoVolume* motherVolume);   // Full-cylinder IRIS geometry with 3 inclined walls
 void createIRISGeometryFullCylwithDisks(TGeoVolume* motherVolume); // Full-cylinder IRIS geometry (no petals, no gaps, no side walls) incl. disks
 void createIRIS4Geometry(TGeoVolume* motherVolume);                // 4 petals, cylindrical L0
 void createIRIS4aGeometry(TGeoVolume* motherVolume);               // 3 petals, cylindrical L0
diff --git a/Detectors/Upgrades/ALICE3/TRK/simulation/src/Detector.cxx b/Detectors/Upgrades/ALICE3/TRK/simulation/src/Detector.cxx
index 556b016f22553..035ad02a68876 100644
--- a/Detectors/Upgrades/ALICE3/TRK/simulation/src/Detector.cxx
+++ b/Detectors/Upgrades/ALICE3/TRK/simulation/src/Detector.cxx
@@ -275,6 +275,10 @@ void Detector::createGeometry()
       LOG(info) << "Building VD with IRIS fully cylindrical layout";
       o2::trk::createIRISGeometryFullCyl(vTRK);
       break;
+    case kIRISFullCyl3InclinedWalls:
+      LOG(info) << "Building VD with IRIS fully cylindrical layout with 3 inclined walls";
+      o2::trk::createIRISGeometry3InclinedWalls(vTRK);
+      break;
     case kIRIS5:
       LOG(info) << "Building VD with IRIS5 layout";
       o2::trk::createIRIS5Geometry(vTRK);
diff --git a/Detectors/Upgrades/ALICE3/TRK/simulation/src/VDGeometryBuilder.cxx b/Detectors/Upgrades/ALICE3/TRK/simulation/src/VDGeometryBuilder.cxx
index b06faa38211bb..643a6bdd94808 100644
--- a/Detectors/Upgrades/ALICE3/TRK/simulation/src/VDGeometryBuilder.cxx
+++ b/Detectors/Upgrades/ALICE3/TRK/simulation/src/VDGeometryBuilder.cxx
@@ -10,7 +10,6 @@
 // or submit itself to any jurisdiction.
 
 #include "TRKSimulation/VDGeometryBuilder.h"
-
 #include <TGeoVolume.h>
 #include <TGeoMatrix.h>
 #include <TGeoTube.h>
@@ -19,13 +18,13 @@
 #include <TGeoCompositeShape.h>
 #include <TString.h>
 #include <DetectorsBase/MaterialManager.h>
-
 #include "TGeoManager.h"
-
 #include "Framework/Logger.h"
 #include "TRKBase/GeometryTGeo.h"
 #include "TRKSimulation/VDLayer.h"
 #include "TRKSimulation/VDSensorRegistry.h"
+#include <algorithm>
+#include <cmath>
 
 namespace o2::trk
 {
@@ -82,6 +81,9 @@ inline bool isSolidToCut(const TGeoVolume* v)
   if (TString(nm).BeginsWith("IRIS_Service_Pos_InVac")) {
     return true;
   }
+  if (TString(nm).BeginsWith("VD_InclinedWall")) {
+    return true;
+  }
   return false;
 }
 
@@ -253,7 +255,17 @@ static constexpr double kPetalZ_cm = 70.0f;          // full wall height
 static constexpr double kWallThick_cm = 0.015f;      // 0.15 mm
 static constexpr double kInnerWallRadius_cm = 0.48f; // 4.8 mm (ALWAYS cylindrical)
 static constexpr double kOuterWallRadius_cm = 3.0f;  // 30 mm (can be changed)
-static constexpr double kEps_cm = 1.e-4f;
+static constexpr double kEps_cm = 2.5e-4f;
+
+// 3 inclined walls ("walls") specs for the full-cylinder option
+// Thickness in-plane (cm). This is the short half-dimension of the TGeoBBox in XY.
+static constexpr double kInclinedWallThick_cm = 0.04f; // 0.4 mm
+// Layer-shell thickness used for the gap boundaries in the inclined-wall construction (cm)
+static constexpr double kSiLayerThick_cm = 0.01f; // 0.1 mm
+// Base tangency angle (deg) for the first wall; the other 2 are +120/+240.
+// This matches the angle used in the ROOT sketch from our chat.
+static constexpr double kInclinedWallPhi0_deg = 27.799f;
+static constexpr double kInclinedWallRmax_cm = 4.75f; // 47.5 mm outer extension
 
 // Coldplate specs (cm)
 static constexpr double kColdplateRadius_cm = 2.6f;     // 26 mm (outer radius)
@@ -806,6 +818,158 @@ static TGeoVolume* buildFullCylAssembly(int petalID, bool withDisks)
   return petalAsm;
 }
 
+// Add 3 inclined walls (straight walls) into a full-cylinder petal assembly.
+// The walls are implemented as TWO TGeoBBox segments per wall, living in the gaps:
+//   - segment 01: from tangency at Rtan to inner surface of L1
+//   - segment 12: from outer surface of L1 to inner surface of L2
+// The construction accounts for the finite wall thickness (kInclinedWallThick_cm).
+static void addInclinedWalls3FullCyl(TGeoVolume* petalAsm, double phi0_deg = kInclinedWallPhi0_deg)
+{
+  if (!petalAsm) {
+    LOGP(error, "addInclinedWalls3FullCyl: petalAsm is null");
+    return;
+  }
+
+  auto& matmgr = o2::base::MaterialManager::Instance();
+  const TGeoMedium* med = matmgr.getTGeoMedium("ALICE3_TRKSERVICES_ALUMINIUM5083");
+  if (!med) {
+    LOGP(warning, "addInclinedWalls3FullCyl: ALICE3_TRKSERVICES_ALUMINIUM5083 not found, walls not created.");
+    return;
+  }
+
+  // Clearance margin from layer/coldplate surfaces (cm)
+  constexpr double clearanceMargin = 0.010; // 100 microns
+
+  // Geometry inputs (cm)
+  constexpr double R0 = rL0_cm;
+  constexpr double R1 = rL1_cm;
+  constexpr double R2 = rL2_cm;
+  constexpr double Rmax = kInclinedWallRmax_cm;
+
+  const double wallDy = 0.5 * kInclinedWallThick_cm;
+  const double shellTh = kSiLayerThick_cm; // 0.1 mm shell thickness for bounds
+  const double h = 0.5 * shellTh;
+  const double dz = 0.5 * kLenZ_cm; // match barrel/coldplate length in full-cyl option
+
+  constexpr int nWalls = 3;
+  constexpr double dPhi = 360.0 / double(nWalls);
+
+  // Gap boundaries (shell surfaces)
+  const double R0_out = R0 + h;
+  const double R1_in = R1 - h;
+  const double R1_out = R1 + h;
+  const double R2_in = R2 - h;
+  const double R2_out = R2 + h;
+
+  // Coldplate outer radius (tube segment is [kColdplateRadius_cm, kColdplateRadius_cm + kColdplateThickness_cm])
+  const double Rcold_out = kColdplateRadius_cm + kColdplateThickness_cm;
+
+  // Tangency radius choice (thickness-safe at s=0): need Rtan - wallDy >= R0_out
+  const double Rtan = R0_out + wallDy + clearanceMargin;
+
+  // For finite-thickness box:
+  //   outermost edge uses Reff_plus, innermost edge uses Reff_minus
+  const double Reff_plus = Rtan + wallDy + clearanceMargin;
+  const double Reff_minus = std::max(0.0, Rtan - wallDy - clearanceMargin);
+
+  auto sAt = [](double R, double Reff) -> double {
+    const double v = R * R - Reff * Reff;
+    return (v > 0.0) ? std::sqrt(v) : 0.0;
+  };
+
+  // Segment bounds in 's' (thickness-safe):
+  // 01: from tangency to L1 inner surface (outer edge <= R1_in)
+  const double sa01 = 0.0;
+  const double sb01 = sAt(R1_in, Reff_plus);
+
+  // 12: from outside L1 to inside L2
+  const double sa12 = sAt(R1_out, Reff_minus); // inner edge >= R1_out
+  const double sb12 = sAt(R2_in, Reff_plus);   // outer edge <= R2_in
+
+  // 23: from outside coldplate (and outside L2) to Rmax
+  const double R23_start = std::max(R2_out, Rcold_out) + clearanceMargin;
+  const double sa23 = sAt(R23_start, Reff_minus); // inner edge >= start radius
+  const double sb23 = sAt(Rmax, Reff_plus);       // outer edge <= Rmax
+
+  if (!((sb01 > sa01) && (sb12 > sa12) && (sb23 > sa23))) {
+    LOGP(error,
+         "addInclinedWalls3FullCyl: invalid bounds. 01:[{},{}] 12:[{},{}] 23:[{},{}] "
+         "Rtan={} Reff-={} Reff+={} R23_start={}",
+         sa01, sb01, sa12, sb12, sa23, sb23,
+         Rtan, Reff_minus, Reff_plus, R23_start);
+    return;
+  }
+
+  // Half-lengths and center parameters (s-centers)
+  const double dx01 = 0.5 * (sb01 - sa01);
+  const double dx12 = 0.5 * (sb12 - sa12);
+  const double dx23 = 0.5 * (sb23 - sa23);
+
+  const double sc01 = 0.5 * (sa01 + sb01);
+  const double sc12 = 0.5 * (sa12 + sb12);
+  const double sc23 = 0.5 * (sa23 + sb23);
+
+  // Create shapes once, reuse for all walls
+  auto* sh01 = new TGeoBBox(dx01, wallDy, dz);
+  auto* sh12 = new TGeoBBox(dx12, wallDy, dz);
+  auto* sh23 = new TGeoBBox(dx23, wallDy, dz);
+  sh01->SetName("VD_InclinedWall01_sh");
+  sh12->SetName("VD_InclinedWall12_sh");
+  sh23->SetName("VD_InclinedWall23_sh");
+
+  const double phi0_rad = phi0_deg * TMath::DegToRad();
+
+  for (int i = 0; i < nWalls; ++i) {
+    const double phi = phi0_rad + i * (dPhi * TMath::DegToRad());
+    const double cosPhi = std::cos(phi);
+    const double sinPhi = std::sin(phi);
+
+    // Tangency point on Rtan
+    const double xT = Rtan * cosPhi;
+    const double yT = Rtan * sinPhi;
+
+    // Tangent direction u = (-sin, cos)
+    const double ux = -sinPhi;
+    const double uy = cosPhi;
+
+    // Centers (in XY)
+    const double cx01 = xT + sc01 * ux;
+    const double cy01 = yT + sc01 * uy;
+    const double cx12 = xT + sc12 * ux;
+    const double cy12 = yT + sc12 * uy;
+    const double cx23 = xT + sc23 * ux;
+    const double cy23 = yT + sc23 * uy;
+
+    // Rotation: local X along tangent => angle = phi + 90°
+    const double alpha_deg = phi0_deg + i * dPhi + 90.0;
+    auto* rot = new TGeoRotation();
+    rot->RotateZ(alpha_deg);
+
+    // Create volumes per wall (unique names)
+    auto* v01 = new TGeoVolume(Form("VD_InclinedWall01_%d", i), sh01, med);
+    auto* v12 = new TGeoVolume(Form("VD_InclinedWall12_%d", i), sh12, med);
+    auto* v23 = new TGeoVolume(Form("VD_InclinedWall23_%d", i), sh23, med);
+    v01->SetLineColor(kOrange + 7);
+    v12->SetLineColor(kOrange + 7);
+    v23->SetLineColor(kOrange + 7);
+    v01->SetTransparency(70);
+    v12->SetTransparency(70);
+    v23->SetTransparency(70);
+
+    auto* T01 = new TGeoCombiTrans(cx01, cy01, 0.0, rot);
+    auto* T12 = new TGeoCombiTrans(cx12, cy12, 0.0, new TGeoRotation(*rot));
+    auto* T23 = new TGeoCombiTrans(cx23, cy23, 0.0, new TGeoRotation(*rot));
+
+    petalAsm->AddNode(v01, 1, T01);
+    petalAsm->AddNode(v12, 1, T12);
+    petalAsm->AddNode(v23, 1, T23);
+
+    LOGP(debug,
+         "InclinedWall {}: 01({:.3f},{:.3f}) 12({:.3f},{:.3f}) 23({:.3f},{:.3f}) angle={:.2f}°",
+         i, cx01, cy01, cx12, cy12, cx23, cy23, alpha_deg);
+  }
+}
+
 // =================== Public entry points ===================
 
 void createIRIS4Geometry(TGeoVolume* motherVolume)
@@ -908,6 +1072,31 @@ void createIRISGeometryFullCyl(TGeoVolume* motherVolume)
   buildIrisCutoutFromPetalSolid(nPetals);
 }
 
+void createIRISGeometry3InclinedWalls(TGeoVolume* motherVolume)
+{
+  if (!motherVolume) {
+    LOGP(error, "createIRISGeometry3InclinedWalls: motherVolume is null");
+    return;
+  }
+
+  clearVDSensorRegistry();
+
+  constexpr int nPetals = 1;
+  constexpr int petalID = 0;
+
+  // Start from the same content as createIRISGeometryFullCyl
+  auto* petal = buildFullCylAssembly(petalID, /*withDisks=*/false);
+
+  // Add the 3 inclined walls into the same assembly
+  addInclinedWalls3FullCyl(petal, kInclinedWallPhi0_deg);
+
+  motherVolume->AddNode(petal, 1, nullptr);
+
+  // Same cutout pipeline as full-cyl
+  buildPetalSolidsComposite(petal);
+  buildIrisCutoutFromPetalSolid(nPetals);
+}
+
 void createIRISGeometryFullCylwithDisks(TGeoVolume* motherVolume)
 {
   if (!motherVolume) {