diff --git a/hdf5-types/src/array.rs b/hdf5-types/src/array.rs
index f5b8956c5..cf0909246 100644
--- a/hdf5-types/src/array.rs
+++ b/hdf5-types/src/array.rs
@@ -142,6 +142,11 @@ impl<T: Copy + fmt::Debug> fmt::Debug for VarLenArray<T> {
     }
 }
 
+// Safety: Memory backed by `VarLenArray` can be accessed and freed from any thread
+unsafe impl<T: Copy + Send> Send for VarLenArray<T> {}
+// Safety: `VarLenArray` has no interior mutability
+unsafe impl<T: Copy + Sync> Sync for VarLenArray<T> {}
+
 #[cfg(test)]
 pub mod tests {
     use super::VarLenArray;
diff --git a/hdf5-types/src/string.rs b/hdf5-types/src/string.rs
index 5f587f500..612f462c7 100644
--- a/hdf5-types/src/string.rs
+++ b/hdf5-types/src/string.rs
@@ -282,6 +282,11 @@ impl AsAsciiStr for VarLenAscii {
     }
 }
 
+// Safety: Memory backed by `VarLenAscii` can be accessed and freed from any thread
+unsafe impl Send for VarLenAscii {}
+// Safety: `VarLenAscii` has no interior mutability
+unsafe impl Sync for VarLenAscii {}
+
 // ================================================================================
 
 #[repr(C)]
@@ -371,6 +376,11 @@ impl FromStr for VarLenUnicode {
     }
 }
 
+// Safety: Memory backed by `VarLenUnicode` can be accessed and freed from any thread
+unsafe impl Send for VarLenUnicode {}
+// Safety: `VarLenUnicode` has no interior mutability
+unsafe impl Sync for VarLenUnicode {}
+
 // ================================================================================
 
 #[repr(C)]