diff --git a/packages/modeling/bench/splitPolygon.bench.js b/packages/modeling/bench/splitPolygon.bench.js
new file mode 100644
index 000000000..364872640
--- /dev/null
+++ b/packages/modeling/bench/splitPolygon.bench.js
@@ -0,0 +1,143 @@
+/**
+ * Direct benchmark for splitPolygonByPlane - the hot path in boolean operations
+ *
+ * Run with: node --expose-gc bench/splitPolygon.bench.js
+ */
+
+const { sphere, torus } = require('../src/primitives')
+const splitPolygonByPlane = require('../src/operations/booleans/trees/splitPolygonByPlane')
+const poly3 = require('../src/geometries/poly3')
+const plane = require('../src/maths/plane')
+
+// Benchmark helper
+const benchmark = (name, setup, fn, iterations = 1000) => {
+  const data = setup()
+
+  // Force GC if available
+  if (global.gc) global.gc()
+
+  // Warmup
+  for (let i = 0; i < 100; i++) fn(data)
+
+  if (global.gc) global.gc()
+  const heapBefore = process.memoryUsage().heapUsed
+
+  const start = process.hrtime.bigint()
+  for (let i = 0; i < iterations; i++) {
+    fn(data)
+  }
+  const end = process.hrtime.bigint()
+
+  if (global.gc) global.gc()
+  const heapAfter = process.memoryUsage().heapUsed
+
+  const totalNs = Number(end - start)
+  const avgNs = totalNs / iterations
+  const avgUs = avgNs / 1000
+  const heapDelta = (heapAfter - heapBefore) / 1024
+
+  console.log(`${name.padEnd(50)} ${avgUs.toFixed(2).padStart(8)} µs/op  heap: ${heapDelta > 0 ? '+' : ''}${heapDelta.toFixed(0)} KB`)
+  return avgUs
+}
+
+console.log('='.repeat(80))
+console.log('splitPolygonByPlane Direct Benchmark')
+console.log('='.repeat(80))
+console.log()
+
+// Get polygons from a sphere
+const testSphere = sphere({ radius: 5, segments: 32 })
+const polygons = testSphere.polygons
+
+console.log(`Test geometry: sphere(32) with ${polygons.length} polygons`)
+console.log(`Average vertices per polygon: ${(polygons.reduce((sum, p) => sum + p.vertices.length, 0) / polygons.length).toFixed(1)}`)
+console.log()
+
+// Test 1: Coplanar case (fast path - type 0 or 1)
+console.log('--- Coplanar Cases (fast path) ---')
+benchmark('coplanar-front (type 0)', () => {
+  const polygon = polygons[0]
+  const pplane = poly3.plane(polygon)
+  return { polygon, splane: pplane }
+}, (data) => splitPolygonByPlane(data.splane, data.polygon), 10000)
+
+// Test 2: Entirely front (type 2)
+console.log()
+console.log('--- One-side Cases (no split needed) ---')
+benchmark('entirely front (type 2)', () => {
+  const polygon = polygons[0]
+  // Create a plane far behind the polygon
+  const splane = [0, 0, 1, -100]
+  return { polygon, splane }
+}, (data) => splitPolygonByPlane(data.splane, data.polygon), 10000)
+
+benchmark('entirely back (type 3)', () => {
+  const polygon = polygons[0]
+  // Create a plane far in front of the polygon
+  const splane = [0, 0, 1, 100]
+  return { polygon, splane }
+}, (data) => splitPolygonByPlane(data.splane, data.polygon), 10000)
+
+// Test 3: Spanning case (type 4) - this is where allocations hurt
+console.log()
+console.log('--- Spanning Cases (allocations happen here) ---')
+benchmark('spanning split (type 4) - triangle', () => {
+  // A triangle that will be split
+  const polygon = poly3.create([[0, 0, 0], [10, 0, 0], [5, 10, 0]])
+  const splane = [1, 0, 0, 5] // Split down the middle
+  return { polygon, splane }
+}, (data) => splitPolygonByPlane(data.splane, data.polygon), 10000)
+
+benchmark('spanning split (type 4) - quad', () => {
+  const polygon = poly3.create([[0, 0, 0], [10, 0, 0], [10, 10, 0], [0, 10, 0]])
+  const splane = [1, 0, 0, 5]
+  return { polygon, splane }
+}, (data) => splitPolygonByPlane(data.splane, data.polygon), 10000)
+
+benchmark('spanning split (type 4) - hexagon', () => {
+  const polygon = poly3.create([
+    [0, 0, 0], [5, 0, 0], [7.5, 4, 0],
+    [5, 8, 0], [0, 8, 0], [-2.5, 4, 0]
+  ])
+  const splane = [1, 0, 0, 2.5]
+  return { polygon, splane }
+}, (data) => splitPolygonByPlane(data.splane, data.polygon), 10000)
+
+// Test 4: Realistic mix from actual boolean operation
+console.log()
+console.log('--- Realistic Mix (simulating boolean op) ---')
+benchmark('mixed types from sphere polygons', () => {
+  // Use multiple polygons with a plane that hits various cases
+  const splane = [0.577, 0.577, 0.577, 0] // Diagonal plane through origin
+  return { polygons: polygons.slice(0, 50), splane }
+}, (data) => {
+  let spanning = 0
+  for (const polygon of data.polygons) {
+    const result = splitPolygonByPlane(data.splane, polygon)
+    if (result.type === 4) spanning++
+  }
+  return spanning
+}, 1000)
+
+// Measure allocation overhead specifically
+console.log()
+console.log('--- Allocation Stress Test ---')
+benchmark('10k spanning splits (allocation heavy)', () => {
+  const polygon = poly3.create([[0, 0, 0], [10, 0, 0], [10, 10, 0], [0, 10, 0]])
+  const splane = [1, 0, 0, 5]
+  return { polygon, splane }
+}, (data) => {
+  for (let i = 0; i < 100; i++) {
+    splitPolygonByPlane(data.splane, data.polygon)
+  }
+}, 100)
+
+console.log()
+console.log('='.repeat(80))
+console.log('Benchmark complete')
+console.log()
+console.log('Note: "spanning split" cases allocate the most:')
+console.log('  - result object { type, front, back }')
+console.log('  - vertexIsBack[] array')
+console.log('  - frontvertices[] and backvertices[] arrays')
+console.log('  - Two new poly3 objects (front and back)')
diff --git a/packages/modeling/src/operations/booleans/trees/splitPolygonByPlane.js b/packages/modeling/src/operations/booleans/trees/splitPolygonByPlane.js
index d8dfb8dec..af42d0b30 100644
--- a/packages/modeling/src/operations/booleans/trees/splitPolygonByPlane.js
+++ b/packages/modeling/src/operations/booleans/trees/splitPolygonByPlane.js
@@ -9,14 +9,26 @@ const splitLineSegmentByPlane = require('./splitLineSegmentByPlane')
 
 const EPS_SQUARED = EPS * EPS
 
+// Object pool for reducing allocations in hot path.
+// The result object is safe to reuse because callers extract front/back immediately.
+// The temporary arrays are only used within splitPolygonByPlane.
+const pool = {
+  result: { type: null, front: null, back: null },
+  vertexIsBack: new Array(64), // Pre-allocated, grows if needed
+  frontvertices: new Array(32),
+  backvertices: new Array(32)
+}
+
 // Remove consecutive duplicate vertices from a polygon vertex list.
 // Compares last vertex to first to handle wraparound.
-// Returns a new array (does not modify input).
-// IMPORTANT: Caller must ensure vertices.length >= 3 before calling.
-const removeConsecutiveDuplicates = (vertices) => {
+// Returns a new array (polygon vertices must be fresh arrays since they're stored in geometry).
+// Accepts optional count parameter for use with pre-allocated pooled arrays.
+const removeConsecutiveDuplicates = (vertices, count) => {
+  const vertexCount = count !== undefined ? count : vertices.length
+  if (vertexCount < 3) return vertices.slice(0, vertexCount)
   const result = []
-  let prevvertex = vertices[vertices.length - 1]
-  for (let i = 0; i < vertices.length; i++) {
+  let prevvertex = vertices[vertexCount - 1]
+  for (let i = 0; i < vertexCount; i++) {
     const vertex = vertices[i]
     if (vec3.squaredDistance(vertex, prevvertex) >= EPS_SQUARED) {
       result.push(vertex)
@@ -36,12 +48,15 @@ const removeConsecutiveDuplicates = (vertices) => {
 // In case the polygon is spanning, returns:
 // .front: a Polygon3 of the front part
 // .back: a Polygon3 of the back part
+//
+// IMPORTANT: The returned object is reused between calls to reduce allocations.
+// Callers must extract .front and .back before the next call to splitPolygonByPlane.
 const splitPolygonByPlane = (splane, polygon) => {
-  const result = {
-    type: null,
-    front: null,
-    back: null
-  }
+  const result = pool.result
+  result.type = null
+  result.front = null
+  result.back = null
+
   // cache in local lets (speedup):
   const vertices = polygon.vertices
   const numvertices = vertices.length
@@ -51,12 +66,16 @@ const splitPolygonByPlane = (splane, polygon) => {
   } else {
     let hasfront = false
     let hasback = false
-    const vertexIsBack = []
+    // Use pooled array, grow if needed
+    let vertexIsBack = pool.vertexIsBack
+    if (vertexIsBack.length < numvertices) {
+      vertexIsBack = pool.vertexIsBack = new Array(numvertices * 2)
+    }
     const MINEPS = -EPS
     for (let i = 0; i < numvertices; i++) {
       const t = vec3.dot(splane, vertices[i]) - splane[3]
       const isback = (t < MINEPS)
-      vertexIsBack.push(isback)
+      vertexIsBack[i] = isback
       if (t > EPS) hasfront = true
       if (t < MINEPS) hasback = true
     }
@@ -71,8 +90,19 @@ const splitPolygonByPlane = (splane, polygon) => {
     } else {
       // spanning
       result.type = 4
-      const frontvertices = []
-      const backvertices = []
+      // Use pooled arrays, grow if needed (max 2 vertices added per original vertex)
+      const maxVerts = numvertices * 2
+      let frontvertices = pool.frontvertices
+      let backvertices = pool.backvertices
+      if (frontvertices.length < maxVerts) {
+        frontvertices = pool.frontvertices = new Array(maxVerts)
+      }
+      if (backvertices.length < maxVerts) {
+        backvertices = pool.backvertices = new Array(maxVerts)
+      }
+      let frontCount = 0
+      let backCount = 0
+
       let isback = vertexIsBack[0]
       for (let vertexindex = 0; vertexindex < numvertices; vertexindex++) {
         const vertex = vertices[vertexindex]
@@ -82,35 +112,36 @@ const splitPolygonByPlane = (splane, polygon) => {
         if (isback === nextisback) {
           // line segment is on one side of the plane:
           if (isback) {
-            backvertices.push(vertex)
+            backvertices[backCount++] = vertex
           } else {
-            frontvertices.push(vertex)
+            frontvertices[frontCount++] = vertex
           }
         } else {
           // line segment intersects plane:
           const nextpoint = vertices[nextvertexindex]
           const intersectionpoint = splitLineSegmentByPlane(splane, vertex, nextpoint)
           if (isback) {
-            backvertices.push(vertex)
-            backvertices.push(intersectionpoint)
-            frontvertices.push(intersectionpoint)
+            backvertices[backCount++] = vertex
+            backvertices[backCount++] = intersectionpoint
+            frontvertices[frontCount++] = intersectionpoint
           } else {
-            frontvertices.push(vertex)
-            frontvertices.push(intersectionpoint)
-            backvertices.push(intersectionpoint)
+            frontvertices[frontCount++] = vertex
+            frontvertices[frontCount++] = intersectionpoint
+            backvertices[backCount++] = intersectionpoint
           }
         }
         isback = nextisback
       } // for vertexindex
-      // remove consecutive duplicate vertices (check length before calling to avoid function overhead)
-      if (frontvertices.length >= 3) {
-        const frontFiltered = removeConsecutiveDuplicates(frontvertices)
+      // remove consecutive duplicate vertices and create final polygons
+      // We need fresh arrays for the polygon vertices since they become part of the geometry
+      if (frontCount >= 3) {
+        const frontFiltered = removeConsecutiveDuplicates(frontvertices, frontCount)
         if (frontFiltered.length >= 3) {
           result.front = poly3.fromPointsAndPlane(frontFiltered, pplane)
         }
       }
-      if (backvertices.length >= 3) {
-        const backFiltered = removeConsecutiveDuplicates(backvertices)
+      if (backCount >= 3) {
+        const backFiltered = removeConsecutiveDuplicates(backvertices, backCount)
         if (backFiltered.length >= 3) {
           result.back = poly3.fromPointsAndPlane(backFiltered, pplane)
         }