diff --git a/swash/processing/read_swash.py b/swash/processing/read_swash.py
index 53c82a9..c8d0f36 100644
--- a/swash/processing/read_swash.py
+++ b/swash/processing/read_swash.py
@@ -31,17 +31,28 @@ class ReadSwash:
 
     def read_scalar(self, path, const=False):
         if const:
-            return self.read_nohead(path).reshape((self._n_t, self._n_x))[0, :]
-        return self.read_nohead(path).reshape((self._n_t, self._n_x))
+            self._data[path.stem] = self.read_nohead(path).reshape(
+                (self._n_t, self._n_x)
+            )[0, :]
+            return
+        self._data[path.stem] = self.read_nohead(path).reshape(
+            (self._n_t, self._n_x)
+        )
 
     def read_vector(self, path):
-        return self.read_nohead(path).reshape((self._n_t, 2, self._n_x))
+        self._data[path.stem] = self.read_nohead(path).reshape(
+            (self._n_t, 2, self._n_x)
+        )
 
     def read_scalar_lay(self, path):
-        return self.read_nohead(path).reshape((self._n_t, -1, self._n_x))
+        self._data[path.stem] = self.read_nohead(path).reshape(
+            (self._n_t, -1, self._n_x)
+        )
 
     def read_vector_lay(self, path):
-        return self.read_nohead(path).reshape((self._n_t, 2, -1, self._n_x))
+        self._data[path.stem] = self.read_nohead(path).reshape(
+            (self._n_t, 2, -1, self._n_x)
+        )
 
     @property
     def t(self):
@@ -50,3 +61,7 @@ class ReadSwash:
     @property
     def x(self):
         return self._x
+
+    @property
+    def data(self):
+        return self._data
diff --git a/swash/processing/sws_npz.py b/swash/processing/sws_npz.py
index 11961bd..815d138 100644
--- a/swash/processing/sws_npz.py
+++ b/swash/processing/sws_npz.py
@@ -27,16 +27,15 @@ rsws = ReadSwash()
 rsws.read_time(sws_out.joinpath("tsec.dat"))
 rsws.read_x(sws_out.joinpath("xp.dat"))
 
-inp.mkdir(exist_ok=True)
-log.info(f"Wrinting output in '{inp}'")
 log.info("Reading 'dep'")
-np.save(inp.joinpath("dep"), rsws.read_scalar(sws_out.joinpath("dep.dat")))
+rsws.read_scalar(sws_out.joinpath("dep.dat"))
 log.info("Reading 'botl'")
-np.save(
-    inp.joinpath("botl"),
-    rsws.read_scalar(sws_out.joinpath("botl.dat"), const=True),
-)
+rsws.read_scalar(sws_out.joinpath("botl.dat"), const=True)
 log.info("Reading 'watl'")
-np.save(inp.joinpath("watl"), rsws.read_scalar(sws_out.joinpath("watl.dat")))
+rsws.read_scalar(sws_out.joinpath("watl.dat"))
 log.info("Reading 'vel'")
-np.save(inp.joinpath("vel"), rsws.read_vector(sws_out.joinpath("vel.dat")))
+rsws.read_vector(sws_out.joinpath("vel.dat"))
+
+log.info(f"Writing npz file in '{inp}'")
+inp.mkdir(exist_ok=True)
+np.savez_compressed(inp.joinpath("sws"), t=rsws.t, x=rsws.x, **rsws.data)