diff --git a/jaxley/utils/swc.py b/jaxley/utils/swc.py
index fbd0a160a..294ce0f87 100644
--- a/jaxley/utils/swc.py
+++ b/jaxley/utils/swc.py
@@ -1,4 +1,4 @@
-from typing import Optional
+from typing import Callable, List, Optional, Tuple
 from warnings import warn
 
 import numpy as np
@@ -31,7 +31,7 @@ def swc_to_jaxley(
         if pathlen == 0.0:
             warn("Found a segment with length 0. Clipping it to 1.0")
             pathlengths[i] = 1.0
-    radius_fns = _extract_endpoint_radiuses(
+    radius_fns = _radius_generating_fns(
         sorted_branches, content[:, 5], each_length, parents, types
     )
 
@@ -45,7 +45,9 @@ def swc_to_jaxley(
     return parents, pathlengths, radius_fns, types
 
 
-def _split_into_branches_and_sort(content, max_branch_len, sort=True):
+def _split_into_branches_and_sort(
+    content: np.ndarray, max_branch_len: float, sort: bool = True
+) -> Tuple[np.ndarray, np.ndarray]:
     branches, types = _split_into_branches(content)
     branches, types = _split_long_branches(branches, types, content, max_branch_len)
 
@@ -60,7 +62,9 @@ def _split_into_branches_and_sort(content, max_branch_len, sort=True):
     return sorted_branches, sorted_types
 
 
-def _split_long_branches(branches, types, content, max_branch_len):
+def _split_long_branches(
+    branches, types, content, max_branch_len
+) -> Tuple[np.ndarray, np.ndarray]:
     pathlengths = _compute_pathlengths(branches, content[:, 2:5])
     pathlengths = [np.sum(length_traced) for length_traced in pathlengths]
     split_branches = []
@@ -100,7 +104,7 @@ def _split_branch_equally(branch, num_subbranches):
     return branches
 
 
-def _split_into_branches(content):
+def _split_into_branches(content: np.ndarray) -> Tuple[np.ndarray, np.ndarray]:
     prev_ind = None
     prev_type = None
     n_branches = 0
@@ -156,7 +160,10 @@ def _build_parents(all_branches):
     return parents
 
 
-def _extract_endpoint_radiuses(all_branches, radiuses, each_length, parents, types):
+def _radius_generating_fns(
+    all_branches, radiuses, each_length, parents, types
+) -> List[Callable]:
+    """For all branches in a cell, returns callable that return radius given loc."""
     radius_fns = []
     for i, branch in enumerate(all_branches):
         rads_in_branch = radiuses[np.asarray(branch) - 1]
@@ -175,13 +182,15 @@ def _extract_endpoint_radiuses(all_branches, radiuses, each_length, parents, typ
     return radius_fns
 
 
-def _radius_generating_fn(radiuses, each_length):
+def _radius_generating_fn(radiuses: np.ndarray, each_length: np.ndarray) -> Callable:
+    each_length[each_length < 1e-8] = 1e-8
     summed_len = np.sum(each_length)
     cutoffs = np.cumsum(np.concatenate([np.asarray([0]), each_length])) / summed_len
     cutoffs[0] -= 1e-8
     cutoffs[-1] += 1e-8
 
     def radius(loc):
+        """Function which returns the radius via linear interpolation."""
         index = np.digitize(loc, cutoffs, right=False)
         left_rad = radiuses[index - 1]
         right_rad = radiuses[index]