diff --git a/cypress/snapshots/app.cy.ts/heatmap_flip.snap.png b/cypress/snapshots/app.cy.ts/heatmap_flip.snap.png
index 06b2475e0..61e11770f 100644
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diff --git a/cypress/snapshots/app.cy.ts/line_1D.snap.png b/cypress/snapshots/app.cy.ts/line_1D.snap.png
index 27c364289..a9c97423c 100644
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diff --git a/cypress/snapshots/app.cy.ts/line_1D_points.snap.png b/cypress/snapshots/app.cy.ts/line_1D_points.snap.png
index 15ffae297..3e6573676 100644
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diff --git a/cypress/snapshots/app.cy.ts/line_complex_1D.snap.png b/cypress/snapshots/app.cy.ts/line_complex_1D.snap.png
index 831f6fec8..e728680da 100644
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diff --git a/cypress/snapshots/app.cy.ts/line_complex_constant.snap.png b/cypress/snapshots/app.cy.ts/line_complex_constant.snap.png
index f7d863cf7..d093e2328 100644
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diff --git a/cypress/snapshots/app.cy.ts/line_constant.snap.png b/cypress/snapshots/app.cy.ts/line_constant.snap.png
index 86dc6e653..aa87ba803 100644
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diff --git a/cypress/snapshots/app.cy.ts/matrix_1D.snap.png b/cypress/snapshots/app.cy.ts/matrix_1D.snap.png
index 539cf11b0..0fbd84332 100644
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diff --git a/packages/app/src/providers/mock/mock-file.ts b/packages/app/src/providers/mock/mock-file.ts
index 1a5eb3dbb..d32351614 100644
--- a/packages/app/src/providers/mock/mock-file.ts
+++ b/packages/app/src/providers/mock/mock-file.ts
@@ -133,6 +133,9 @@ export function makeMockFile(): GroupWithChildren {
         array('oneD'),
         array('oneD_linear'),
         array('oneD_bigint'),
+        array('oneD_string', {
+          type: strType(H5T_CSET.ASCII, H5T_STR.SPACEPAD, 256),
+        }),
         array('oneD_boolean'),
         array('oneD_enum', {
           type: enumType(intType(false, 8), ENUM_MAPPING),
diff --git a/packages/app/src/vis-packs/core/matrix/utils.ts b/packages/app/src/vis-packs/core/matrix/utils.ts
index bc470611c..678efb85c 100644
--- a/packages/app/src/vis-packs/core/matrix/utils.ts
+++ b/packages/app/src/vis-packs/core/matrix/utils.ts
@@ -104,7 +104,8 @@ export function getCellWidth(
   }
 
   if (type.class === DTypeClass.String) {
-    return type.length !== undefined ? 12 * type.length : 300;
+    // Use length from dtype if available, but with upper bound to avoid large empty cells with padded strings
+    return type.length !== undefined ? Math.min(12 * type.length, 300) : 300;
   }
 
   if (type.class === DTypeClass.Bool) {
diff --git a/packages/shared/src/mock-values.ts b/packages/shared/src/mock-values.ts
index 7f8ec29d9..ed7b80d38 100644
--- a/packages/shared/src/mock-values.ts
+++ b/packages/shared/src/mock-values.ts
@@ -127,6 +127,7 @@ export const mockValues = {
   oneD,
   oneD_linear: () => ndarray(range1()),
   oneD_bigint,
+  oneD_string: () => ndarray(range8().map((val) => 'A'.repeat(val))),
   oneD_complex,
   oneD_compound,
   oneD_boolean,