diff --git a/iso/builder/build.sh b/iso/builder/build.sh
index 0a87a43..a74f425 100755
--- a/iso/builder/build.sh
+++ b/iso/builder/build.sh
@@ -200,9 +200,20 @@ else
 fi
 
 echo "=== preparing staged overlay ==="
+# Preserve lb package cache across builds so apt packages are not re-downloaded.
+LB_PKG_CACHE="${CACHE_ROOT}/lb-packages"
+mkdir -p "${LB_PKG_CACHE}"
+if [ -d "${BUILD_WORK_DIR}/cache/packages.chroot" ]; then
+    rsync -a --delete "${BUILD_WORK_DIR}/cache/packages.chroot/" "${LB_PKG_CACHE}/"
+fi
 rm -rf "${BUILD_WORK_DIR}" "${OVERLAY_STAGE_DIR}"
 mkdir -p "${BUILD_WORK_DIR}" "${OVERLAY_STAGE_DIR}"
 rsync -a "${BUILDER_DIR}/" "${BUILD_WORK_DIR}/"
+# Restore lb package cache
+if [ -d "${LB_PKG_CACHE}" ] && [ "$(ls -A "${LB_PKG_CACHE}" 2>/dev/null)" ]; then
+    mkdir -p "${BUILD_WORK_DIR}/cache/packages.chroot"
+    rsync -a "${LB_PKG_CACHE}/" "${BUILD_WORK_DIR}/cache/packages.chroot/"
+fi
 rsync -a "${OVERLAY_DIR}/" "${OVERLAY_STAGE_DIR}/"
 rm -f \
     "${OVERLAY_STAGE_DIR}/etc/bee-ssh-password-fallback" \