diff --git a/yt_idefix/data_structures.py b/yt_idefix/data_structures.py
index b583829f..8c1cc6a8 100644
--- a/yt_idefix/data_structures.py
+++ b/yt_idefix/data_structures.py
@@ -8,7 +8,7 @@
 from abc import ABC, abstractmethod
 from functools import cached_property
 from pathlib import Path
-from typing import Literal
+from typing import TYPE_CHECKING, Literal
 
 import inifix
 import numpy as np
@@ -29,6 +29,16 @@
 # even though we don't call them directly
 from .io import IdefixDmpIO, IdefixVtkIO, PlutoVtkIO  # noqa
 
+if TYPE_CHECKING:
+    # these should really be unyt_array,
+    # but mypy doesn't recognize it as a valid type as of unyt 2.9.3 and mypy 0.991
+    XSpans = np.ndarray
+    YSpans = np.ndarray
+    ZSpans = np.ndarray
+    XCoords = np.ndarray
+    YCoords = np.ndarray
+    ZCoords = np.ndarray
+
 ytLogger = logging.getLogger("yt")
 
 
@@ -114,14 +124,14 @@ def _get_field_offset_index(self) -> dict[str, int]:
 
     @abstractmethod
     @cached_property
-    def _cell_widths(self):
+    def _cell_widths(self) -> tuple[XSpans, YSpans, ZSpans]:
         # must return a 3-tuple of 1D unyt_array
         # with unit "code_length" and dtype float64
         ...
 
     @abstractmethod
     @cached_property
-    def _cell_centers(self):
+    def _cell_centers(self) -> tuple[XCoords, YCoords, ZCoords]:
         # must return a 3-tuple of 1D unyt_array
         # with unit "code_length" and dtype float64
         ...
@@ -152,35 +162,48 @@ def _get_field_offset_index(self) -> dict[str, int]:
         return self.ds._field_offset_index
 
     @cached_property
-    def _cell_widths(self):
+    def _cell_widths(self) -> tuple[XSpans, YSpans, ZSpans]:
         with open(self.index_filename, "rb") as fh:
             cell_edges = vtk_io.read_grid_coordinates(fh, geometry=self.ds.geometry)
 
-        cell_widths: list[np.ndarray] = []
+        dims = self.ds.domain_dimensions
         length_unit = self.ds.quan(1, "code_length")
+
+        cell_widths: tuple[XSpans, YSpans, ZSpans]
+        cell_widths = (
+            np.empty(max(dims[0], 2), dtype="float64") * length_unit,
+            np.empty(max(dims[1], 2), dtype="float64") * length_unit,
+            np.empty(max(dims[2], 2), dtype="float64") * length_unit,
+        )
+
         for idir, edges in enumerate(cell_edges[:3]):
-            ncells = self.ds.domain_dimensions[idir]
-            if ncells > 1:
-                cell_widths.append(np.ediff1d(edges).astype("float64") * length_unit)
+            if dims[idir] > 1:
+                cell_widths[idir][:] = np.ediff1d(edges)
             else:
-                cell_widths.append(np.array([self.ds.domain_width[idir]]) * length_unit)
-        return tuple(cell_widths)
+                cell_widths[idir][:] = self.ds.domain_width[idir]
+        return cell_widths
 
     @cached_property
-    def _cell_centers(self):
+    def _cell_centers(self) -> tuple[XCoords, YCoords, ZCoords]:
         with open(self.index_filename, "rb") as fh:
             cell_edges = vtk_io.read_grid_coordinates(fh, geometry=self.ds.geometry)
 
-        cell_centers: list[np.ndarray] = []
+        dims = self.ds.domain_dimensions
         length_unit = self.ds.quan(1, "code_length")
+
+        cell_centers: tuple[XCoords, YCoords, ZCoords]
+        cell_centers = (
+            np.empty(max(dims[0], 2), dtype="float64") * length_unit,
+            np.empty(max(dims[1], 2), dtype="float64") * length_unit,
+            np.empty(max(dims[2], 2), dtype="float64") * length_unit,
+        )
+
         for idir, edges in enumerate(cell_edges[:3]):
-            ncells = self.ds.domain_dimensions[idir]
-            if ncells > 1:
-                e64 = edges.astype("float64")
-                cell_centers.append(0.5 * (e64[1:] + e64[:-1]) * length_unit)
+            if dims[idir] > 1:
+                cell_centers[idir][:] = 0.5 * (edges[1:] + edges[:-1])
             else:
-                cell_centers.append(np.array([edges[0]]) * length_unit)
-        return tuple(cell_centers)
+                cell_centers[idir][:] = edges[0]
+        return cell_centers
 
 
 class IdefixDmpHierarchy(IdefixHierarchy):
@@ -189,16 +212,24 @@ def _get_field_offset_index(self) -> dict[str, int]:
             return dmp_io.get_field_offset_index(fh)
 
     @cached_property
-    def _cell_widths(self):
+    def _cell_widths(self) -> tuple[XSpans, YSpans, ZSpans]:
         _fprops, fdata = dmp_io.read_idefix_dmpfile(self.index_filename, skip_data=True)
         length_unit = self.ds.quan(1, "code_length")
-        return tuple((fdata[f"xr{d}"] - fdata[f"xl{d}"]) * length_unit for d in "123")
+        return (
+            (fdata["xr1"] - fdata["xl1"]) * length_unit,
+            (fdata["xr2"] - fdata["xl2"]) * length_unit,
+            (fdata["xr3"] - fdata["xl3"]) * length_unit,
+        )
 
     @cached_property
-    def _cell_centers(self):
+    def _cell_centers(self) -> tuple[XCoords, YCoords, ZCoords]:
         _fprops, fdata = dmp_io.read_idefix_dmpfile(self.index_filename, skip_data=True)
         length_unit = self.ds.quan(1, "code_length")
-        return tuple(fdata[f"x{d}"] * length_unit for d in "123")
+        return (
+            fdata["x1"] * length_unit,
+            fdata["x2"] * length_unit,
+            fdata["x3"] * length_unit,
+        )
 
 
 class IdefixDataset(Dataset, ABC):