diff --git a/src/build123d/exporters.py b/src/build123d/exporters.py
index a229fa2..687e2f1 100644
--- a/src/build123d/exporters.py
+++ b/src/build123d/exporters.py
@@ -34,6 +34,7 @@ import math
 import xml.etree.ElementTree as ET
 from copy import copy
 from enum import Enum, auto
+from io import BytesIO
 from os import PathLike, fsdecode
 from typing import Any, TypeAlias
 from warnings import warn
@@ -636,13 +637,13 @@ class ExportDXF(Export2D):
 
     # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
-    def write(self, file_name: PathLike | str | bytes):
+    def write(self, file_name: PathLike | str | bytes | BytesIO):
         """write
 
         Writes the DXF data to the specified file name.
 
         Args:
-            file_name (PathLike |  str |  bytes): The file name (including path) where
+            file_name (PathLike |  str |  bytes | BytesIO): The file name (including path) where
                 the DXF data will be written.
         """
         # Reset the main CAD viewport of the model space to the
@@ -650,7 +651,12 @@ class ExportDXF(Export2D):
         # https://github.com/gumyr/build123d/issues/382 tracks
         # exposing viewport control to the user.
         zoom.extents(self._modelspace)
-        self._document.saveas(fsdecode(file_name))
+
+        if not isinstance(file_name, BytesIO):
+            file_name = fsdecode(file_name)
+            self._document.saveas(file_name)
+        else:
+            self._document.write(file_name, fmt="bin")
 
     # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
@@ -1497,13 +1503,13 @@ class ExportSVG(Export2D):
 
     # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
-    def write(self, path: PathLike | str | bytes):
+    def write(self, path: PathLike | str | bytes | BytesIO):
         """write
 
         Writes the SVG data to the specified file path.
 
         Args:
-            path (PathLike |  str |  bytes): The file path where the SVG data will be written.
+            path (PathLike | str | bytes | BytesIO): The file path where the SVG data will be written.
         """
         # pylint: disable=too-many-locals
         bb = self._bounds
@@ -1549,5 +1555,9 @@ class ExportSVG(Export2D):
 
         xml = ET.ElementTree(svg)
         ET.indent(xml, "  ")
+
+        if not isinstance(path, BytesIO):
+            path = fsdecode(path)
+
         # xml.write(path, encoding="utf-8", xml_declaration=True, default_namespace=False)
         xml.write(path, encoding="utf-8", xml_declaration=True, default_namespace=None)
diff --git a/src/build123d/exporters3d.py b/src/build123d/exporters3d.py
index 505d4aa..759464a 100644
--- a/src/build123d/exporters3d.py
+++ b/src/build123d/exporters3d.py
@@ -182,7 +182,7 @@ def export_brep(
 
 def export_gltf(
     to_export: Shape,
-    file_path: PathLike | str | bytes | BytesIO,
+    file_path: PathLike | str | bytes,
     unit: Unit = Unit.MM,
     binary: bool = False,
     linear_deflection: float = 0.001,
@@ -198,7 +198,7 @@ def export_gltf(
 
     Args:
         to_export (Shape): object or assembly
-        file_path (Union[PathLike, str, bytes, BytesIO]): glTF file path
+        file_path (Union[PathLike, str, bytes]): glTF file path
         unit (Unit, optional): shape units. Defaults to Unit.MM.
         binary (bool, optional): output format. Defaults to False.
         linear_deflection (float, optional): A linear deflection setting which limits
@@ -234,12 +234,9 @@ def export_gltf(
     # Create the XCAF document
     doc: TDocStd_Document = _create_xde(to_export, unit)
 
-    if not isinstance(file_path, BytesIO):
-        file_path = fsdecode(file_path)
-
     # Write the glTF file
     writer = RWGltf_CafWriter(
-        theFile=TCollection_AsciiString(file_path, theIsBinary=binary
+        theFile=TCollection_AsciiString(fsdecode(file_path)), theIsBinary=binary
     )
     writer.SetParallel(True)
     index_map = TColStd_IndexedDataMapOfStringString()
@@ -330,9 +327,12 @@ def export_step(
     writer.Transfer(doc, STEPControl_StepModelType.STEPControl_AsIs)
 
     if not isinstance(file_path, BytesIO):
-        file_path = fspath(file_path)
+        status = (
+            writer.Write(fspath(file_path)) == IFSelect_ReturnStatus.IFSelect_RetDone
+        )
+    else:
+        status = writer.WriteStream(file_path) == IFSelect_ReturnStatus.IFSelect_RetDone
 
-    status = writer.Write(file_path) == IFSelect_ReturnStatus.IFSelect_RetDone
     if not status:
         raise RuntimeError("Failed to write STEP file")
 
@@ -341,7 +341,7 @@ def export_step(
 
 def export_stl(
     to_export: Shape,
-    file_path: PathLike | str | bytes | BytesIO,
+    file_path: PathLike | str | bytes,
     tolerance: float = 1e-3,
     angular_tolerance: float = 0.1,
     ascii_format: bool = False,
@@ -352,7 +352,7 @@ def export_stl(
 
     Args:
         to_export (Shape): object or assembly
-        file_path (Union[PathLike, str, bytes, BytesIO]): The path and file name to write the STL output to.
+        file_path (Union[PathLike, str, bytes]): The path and file name to write the STL output to.
         tolerance (float, optional): A linear deflection setting which limits the distance
             between a curve and its tessellation. Setting this value too low will result in
             large meshes that can consume computing resources. Setting the value too high can
@@ -374,8 +374,4 @@ def export_stl(
     writer = StlAPI_Writer()
 
     writer.ASCIIMode = ascii_format
-
-    if not isinstance(file_path, BytesIO):
-        file_path = fsdecode(file_path)
-
-    return writer.Write(to_export.wrapped, file_path)
+    return writer.Write(to_export.wrapped, fsdecode(file_path))
diff --git a/src/build123d/mesher.py b/src/build123d/mesher.py
index 5433848..8c4ce42 100644
--- a/src/build123d/mesher.py
+++ b/src/build123d/mesher.py
@@ -83,6 +83,7 @@ license:
 # pylint: disable=no-name-in-module, import-error
 import copy as copy_module
 import ctypes
+from io import BytesIO
 import math
 import os
 import sys
@@ -312,12 +313,12 @@ class Mesher:
         # Round off the vertices to avoid vertices within tolerance being
         # considered as different vertices
         digits = -int(round(math.log(TOLERANCE, 10), 1))
-        
+
         # Create vertex to index mapping directly
         vertex_to_idx = {}
         next_idx = 0
         vert_table = {}
-        
+
         # First pass - create mapping
         for i, (x, y, z) in enumerate(ocp_mesh_vertices):
             key = (round(x, digits), round(y, digits), round(z, digits))
@@ -325,17 +326,16 @@ class Mesher:
                 vertex_to_idx[key] = next_idx
                 next_idx += 1
             vert_table[i] = vertex_to_idx[key]
-        
+
         # Create vertices array in one shot
         vertices_3mf = [
-            Lib3MF.Position((ctypes.c_float * 3)(*v))
-            for v in vertex_to_idx.keys()
+            Lib3MF.Position((ctypes.c_float * 3)(*v)) for v in vertex_to_idx.keys()
         ]
-        
+
         # Pre-allocate triangles array and process in bulk
         c_uint3 = ctypes.c_uint * 3
         triangles_3mf = []
-        
+
         # Process triangles in bulk
         for tri in triangles:
             # Map indices directly without list comprehension
@@ -343,11 +343,13 @@ class Mesher:
             mapped_a = vert_table[a]
             mapped_b = vert_table[b]
             mapped_c = vert_table[c]
-            
+
             # Quick degenerate check without set creation
             if mapped_a != mapped_b and mapped_b != mapped_c and mapped_c != mapped_a:
-                triangles_3mf.append(Lib3MF.Triangle(c_uint3(mapped_a, mapped_b, mapped_c)))
-        
+                triangles_3mf.append(
+                    Lib3MF.Triangle(c_uint3(mapped_a, mapped_b, mapped_c))
+                )
+
         return (vertices_3mf, triangles_3mf)
 
     def _add_color(self, b3d_shape: Shape, mesh_3mf: Lib3MF.MeshObject):
@@ -540,7 +542,7 @@ class Mesher:
         """write
 
         Args:
-            file_name Union[Pathlike, str, bytes]: file path
+            file_name Union[Pathlike, str, bytes, BytesIO]: file path
 
         Raises:
             ValueError: Unknown file format - must be 3mf or stl
@@ -551,3 +553,8 @@ class Mesher:
             raise ValueError(f"Unknown file format {output_file_extension}")
         writer = self.model.QueryWriter(output_file_extension[1:])
         writer.WriteToFile(file_name)
+
+    def write_stream(self, stream: BytesIO, file_type: str):
+        writer = self.model.QueryWriter(file_type)
+        result = bytes(writer.WriteToBuffer())
+        stream.write(result)
diff --git a/tests/test_exporters.py b/tests/test_exporters.py
index f95a92e..11c63da 100644
--- a/tests/test_exporters.py
+++ b/tests/test_exporters.py
@@ -1,3 +1,4 @@
+from io import BytesIO
 from os import fsdecode, fsencode
 from typing import Union, Iterable
 import math
@@ -194,7 +195,9 @@ class ExportersTestCase(unittest.TestCase):
 
 
 @pytest.mark.parametrize(
-    "format", (Path, fsencode, fsdecode), ids=["path", "bytes", "str"]
+    "format",
+    (Path, fsencode, fsdecode),
+    ids=["path", "bytes", "str"],
 )
 @pytest.mark.parametrize("Exporter", (ExportSVG, ExportDXF))
 def test_pathlike_exporters(tmp_path, format, Exporter):
@@ -205,5 +208,14 @@ def test_pathlike_exporters(tmp_path, format, Exporter):
     exporter.write(path)
 
 
+@pytest.mark.parametrize("Exporter", (ExportSVG, ExportDXF))
+def test_exporters_in_memory(Exporter):
+    buffer = BytesIO()
+    sketch = ExportersTestCase.create_test_sketch()
+    exporter = Exporter()
+    exporter.add_shape(sketch)
+    exporter.write(buffer)
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/tests/test_exporters3d.py b/tests/test_exporters3d.py
index 644ac3e..bf1c1bd 100644
--- a/tests/test_exporters3d.py
+++ b/tests/test_exporters3d.py
@@ -206,10 +206,11 @@ def test_pathlike_exporters(tmp_path, format, exporter):
     exporter(box, path)
 
 
-def test_export_brep_in_memory():
+@pytest.mark.parametrize("exporter", (export_step, export_brep))
+def test_exporters_in_memory(exporter):
     buffer = io.BytesIO()
     box = Box(1, 1, 1).locate(Pos(-1, -2, -3))
-    export_brep(box, buffer)
+    exporter(box, buffer)
 
 
 if __name__ == "__main__":
diff --git a/tests/test_mesher.py b/tests/test_mesher.py
index 0be4ccb..59b7214 100644
--- a/tests/test_mesher.py
+++ b/tests/test_mesher.py
@@ -1,4 +1,5 @@
 import unittest, uuid
+from io import BytesIO
 from packaging.specifiers import SpecifierSet
 from pathlib import Path
 from os import fsdecode, fsencode
@@ -237,5 +238,13 @@ def test_pathlike_mesher(tmp_path, format):
     importer.read(path)
 
 
+@pytest.mark.parametrize("file_type", ("3mf", "stl"))
+def test_in_memory_mesher(file_type):
+    stream = BytesIO()
+    exporter = Mesher()
+    exporter.add_shape(Solid.make_box(1, 1, 1))
+    exporter.write_stream(stream, file_type)
+
+
 if __name__ == "__main__":
     unittest.main()