diff --git a/app.py b/app.py
index 19aeee0..bb504b3 100755
--- a/app.py
+++ b/app.py
@@ -8,8 +8,7 @@ import os
 from os.path import join
 import sqlite3
 import uuid
-import tarfile
-from . import db, config, scanner, calibration
+from . import db, config, scanner, calibration, tar
 
 app = Flask(__name__)
 
@@ -277,94 +276,39 @@ def download_object(id: int):
     object = db.Object.get_from_id(id, conn).full(conn)
 
     # Group acquisitions sharing calibration
-
     def keyfunc(x: db.Calibration) -> int:
         return x.calibration_id
 
     acquisitions_sorted = sorted(object.acquisitions, key=keyfunc)
-    acquisitions_grouped = [(db.Calibration.get_from_id(k, conn), list(g)) for k, g in itertools.groupby(acquisitions_sorted, key=keyfunc)]
+    acquisitions_grouped = [
+        (db.Calibration.get_from_id(k, conn), list(g))
+        for k, g in itertools.groupby(acquisitions_sorted, key=keyfunc)
+    ]
 
-    def generate():
-        for calibration_index, (calib, acquisitions) in enumerate(acquisitions_grouped):
-            # Send each image
-            calibration_dir = join(config.CALIBRATION_DIR, str(calib.id))
-            for image in os.listdir(calibration_dir):
+    # Create archive file to send
+    archive = tar.TarSender()
 
-                # Generate tar header for file
-                image_path = join(calibration_dir, image)
-                bytes = io.BytesIO()
-                stat = os.stat(image_path)
+    for calibration_index, (calib, acquisitions) in enumerate(acquisitions_grouped):
+        calibration_dir = join(config.CALIBRATION_DIR, str(calib.id))
 
-                # Create dummy tar to extract tar header for file
-                with tarfile.open(fileobj=bytes, mode='w') as buffer:
-                    tar_info = tarfile.TarInfo(image_path)
-                    tar_info.name = f'object/{calibration_index}/calibration/{image}'
-                    tar_info.size = stat.st_size
-                    buffer.addfile(tar_info)
+        # Add calibration images
+        for image in os.listdir(calibration_dir):
+            archive.add_file(
+                f'object/{calibration_index}/calibration/{image}',
+                join(calibration_dir, image)
+            )
 
-                # Yield header
-                value = bytes.getvalue()
-                yield value[:512]
+        # Add each acquisition
+        for acquisition_index, acquisition in enumerate(acquisitions):
+            acquisition_dir = join(config.OBJECT_DIR, str(object.id), str(acquisition.id))
 
-                # Yield file content, by chunks of 4MiB
-                chunk_size = 4_194_304
-                bytes_len = 0
+            for image in os.listdir(acquisition_dir):
+                archive.add_file(
+                    f'object/{calibration_index}/{acquisition_index}/{image}',
+                    join(acquisition_dir, image)
+                )
 
-                with open(image_path, 'rb') as file:
-                    while True:
-                        bytes = file.read(chunk_size)
-
-                        if len(bytes) == 0:
-                            break
-
-                        bytes_len += len(bytes)
-                        yield bytes
-
-                    yield b'\x00' * (512 - bytes_len % 512)
-
-            for acquisition_index, acquisition in enumerate(acquisitions):
-                acquisition_dir = join(config.OBJECT_DIR, str(object.id), str(acquisition.id))
-
-                # Send each image
-                for image in os.listdir(acquisition_dir):
-
-                    # Generate tar header for file
-                    image_path = join(acquisition_dir, image)
-                    bytes = io.BytesIO()
-                    stat = os.stat(image_path)
-
-                    # Create dummy tar to extract tar header for file
-                    with tarfile.open(fileobj=bytes, mode='w') as buffer:
-                        tar_info = tarfile.TarInfo(image_path)
-                        tar_info.name = f'object/{calibration_index}/{acquisition_index}/{image}'
-                        tar_info.size = stat.st_size
-                        buffer.addfile(tar_info)
-
-                    # Yield header
-                    value = bytes.getvalue()
-                    yield value[:512]
-
-                    # Yield file content, by chunks of 4MiB
-                    chunk_size = 4_194_304
-                    bytes_len = 0
-
-                    with open(image_path, 'rb') as file:
-                        while True:
-                            bytes = file.read(chunk_size)
-
-                            if len(bytes) == 0:
-                                break
-
-                            bytes_len += len(bytes)
-                            yield bytes
-
-                        yield b'\x00' * (512 - bytes_len % 512)
-
-    return app.response_class(
-        generate(),
-        mimetype='application/x-tar',
-        headers={'Content-Disposition': 'attachment; filename="archive.tar"'}
-    )
+    return archive.response()
 
 
 @app.route('/static/<path:path>')
diff --git a/tar.py b/tar.py
new file mode 100644
index 0000000..ef09d50
--- /dev/null
+++ b/tar.py
@@ -0,0 +1,58 @@
+from flask import Response
+import io
+import os
+import tarfile
+
+# 4MiB chuns
+CHUNK_SIZE = 4_194_304
+
+
+def header_chunk(filename: str, filepath: str) -> bytes:
+    bytes = io.BytesIO()
+    stat = os.stat(filepath)
+
+    # Create dummy tar to extract tar header for file
+    with tarfile.open(fileobj=bytes, mode='w') as buffer:
+        tar_info = tarfile.TarInfo(filepath)
+        tar_info.name = filename
+        tar_info.size = stat.st_size
+        buffer.addfile(tar_info)
+
+    # TODO if we were able to build this chunk without tarfile, it would avoid
+    # whole file copy in memory
+    return bytes.getvalue()[:512]
+
+
+class TarSender:
+    def __init__(self):
+        self.files: dict[str, str] = {}
+
+    def add_file(self, filename: str, filepath: str):
+        self.files[filename] = filepath
+
+    def response(self):
+        def generate():
+            for name, file in self.files.items():
+                yield header_chunk(name, file)
+
+                bytes_sent = 0
+
+                with open(file, 'rb') as f:
+                    while True:
+                        bytes = f.read(CHUNK_SIZE)
+
+                        if len(bytes) == 0:
+                            break
+
+                        bytes_sent += len(bytes)
+                        yield bytes
+
+                    # Because tar use records of 512 bytes, we need to pad the
+                    # file with zeroes to fill the last chunk
+                    yield b'\x00' * (512 - bytes_sent % 512)
+
+        return Response(
+            generate(),
+            mimetype='application/x-tar',
+            headers={'Content-Disposition': 'attachment; filename="archive.tar"'}
+        )