diff --git a/packages/super-editor/src/core/super-converter/v3/handlers/w/tblGrid/tblGrid-translator.js b/packages/super-editor/src/core/super-converter/v3/handlers/w/tblGrid/tblGrid-translator.js
index ecf0a4dbb1..f90685d244 100644
--- a/packages/super-editor/src/core/super-converter/v3/handlers/w/tblGrid/tblGrid-translator.js
+++ b/packages/super-editor/src/core/super-converter/v3/handlers/w/tblGrid/tblGrid-translator.js
@@ -47,7 +47,7 @@ const decode = (params) => {
   const grid = Array.isArray(rawGrid) ? rawGrid : [];
   const { firstRow = {}, preferTableGrid = false, totalColumns: requestedColumns } = params.extraParams || {};
 
-  const cellNodes = firstRow.content?.filter((n) => n.type === 'tableCell') ?? [];
+  const cellNodes = firstRow.content?.filter((n) => n.type === 'tableCell' || n.type === 'tableHeader') ?? [];
 
   let colWidthsFromCellNodes = cellNodes.flatMap((cell) => {
     const spanCount = Math.max(1, cell?.attrs?.colspan ?? 1);
diff --git a/packages/super-editor/src/core/super-converter/v3/handlers/w/tblGrid/tblGrid-translator.test.js b/packages/super-editor/src/core/super-converter/v3/handlers/w/tblGrid/tblGrid-translator.test.js
index 59738d1fdb..3d6618a929 100644
--- a/packages/super-editor/src/core/super-converter/v3/handlers/w/tblGrid/tblGrid-translator.test.js
+++ b/packages/super-editor/src/core/super-converter/v3/handlers/w/tblGrid/tblGrid-translator.test.js
@@ -322,6 +322,28 @@ describe('w:tblGrid translator', () => {
       expect(widths).toEqual(['2000', '4000']);
     });
 
+    it('derives grid widths from tableHeader cells in header-only first row', () => {
+      const params = {
+        node: {
+          attrs: {},
+        },
+        extraParams: {
+          firstRow: {
+            content: [
+              { type: 'tableHeader', attrs: { colspan: 1, colwidth: [80] } },
+              { type: 'tableHeader', attrs: { colspan: 1, colwidth: [120] } },
+            ],
+          },
+        },
+      };
+
+      const result = translator.decode(params);
+      expect(result.name).toBe('w:tblGrid');
+      const widths = result.elements.map((el) => el.attributes['w:w']);
+      // 80 * 20 = 1600, 120 * 20 = 2400 (via mocked pixelsToTwips)
+      expect(widths).toEqual(['1600', '2400']);
+    });
+
     it('preserves narrow grid columns for placeholder cells without inflating width', () => {
       const params = {
         node: {
diff --git a/packages/super-editor/src/core/super-converter/v3/handlers/w/tc/helpers/translate-table-cell.js b/packages/super-editor/src/core/super-converter/v3/handlers/w/tc/helpers/translate-table-cell.js
index 8f411ceb5e..147ff39f3c 100644
--- a/packages/super-editor/src/core/super-converter/v3/handlers/w/tc/helpers/translate-table-cell.js
+++ b/packages/super-editor/src/core/super-converter/v3/handlers/w/tc/helpers/translate-table-cell.js
@@ -39,15 +39,28 @@ export function generateTableCellProperties(node) {
   const { attrs } = node;
 
   // Width
-  const { colwidth = [], cellWidthType = 'dxa', widthUnit } = attrs;
-  const colwidthSum = colwidth.reduce((acc, curr) => acc + curr, 0);
-  const propertiesWidthPixels = twipsToPixels(tableCellProperties.cellWidth?.value);
-  if (propertiesWidthPixels !== colwidthSum) {
-    // If the value has changed, update it
-    tableCellProperties['cellWidth'] = {
-      value: widthUnit === 'px' ? pixelsToTwips(colwidthSum) : inchesToTwips(colwidthSum),
-      type: cellWidthType,
-    };
+  const { colwidth: rawColwidth, widthUnit = 'px' } = attrs;
+  const resolvedWidthType =
+    attrs.cellWidthType ??
+    (attrs.widthType !== 'auto' ? attrs.widthType : undefined) ??
+    tableCellProperties.cellWidth?.type ??
+    'dxa';
+
+  // Filter to finite numbers to guard against NaN/Infinity/non-numeric entries
+  const colwidth = Array.isArray(rawColwidth) ? rawColwidth.filter((v) => Number.isFinite(v)) : [];
+
+  // Skip rewrite when:
+  // - colwidth is empty (no data to compute from — preserve original cellWidth)
+  // - resolvedWidthType is 'pct' (colwidth is in pixels but type expects fiftieths-of-percent)
+  if (colwidth.length > 0 && resolvedWidthType !== 'pct') {
+    const colwidthSum = colwidth.reduce((acc, curr) => acc + curr, 0);
+    const propertiesWidthPixels = twipsToPixels(tableCellProperties.cellWidth?.value);
+    if (propertiesWidthPixels !== colwidthSum) {
+      tableCellProperties['cellWidth'] = {
+        value: widthUnit === 'px' ? pixelsToTwips(colwidthSum) : inchesToTwips(colwidthSum),
+        type: resolvedWidthType,
+      };
+    }
   }
 
   // Colspan
diff --git a/packages/super-editor/src/core/super-converter/v3/handlers/w/tc/helpers/translate-table-cell.test.js b/packages/super-editor/src/core/super-converter/v3/handlers/w/tc/helpers/translate-table-cell.test.js
index a4d682c56f..10d44cfbcb 100644
--- a/packages/super-editor/src/core/super-converter/v3/handlers/w/tc/helpers/translate-table-cell.test.js
+++ b/packages/super-editor/src/core/super-converter/v3/handlers/w/tc/helpers/translate-table-cell.test.js
@@ -96,3 +96,118 @@ describe('translate-table-cell helpers', () => {
     expect(out.elements[1]).toMatchObject({ name: 'w:p' });
   });
 });
+
+/** Helper: extract w:tcW element from a generateTableCellProperties result */
+function getTcW(tcPr) {
+  return tcPr.elements?.find((e) => e.name === 'w:tcW') ?? null;
+}
+
+describe('IT-550: tableHeader width export fixes', () => {
+  it('uses pixelsToTwips when widthUnit is px', () => {
+    const node = { attrs: { colwidth: [100], widthUnit: 'px' } };
+    const tcPr = generateTableCellProperties(node);
+    const tcW = getTcW(tcPr);
+    expect(tcW.attributes['w:w']).toBe(String(pixelsToTwips(100)));
+    expect(tcW.attributes['w:type']).toBe('dxa');
+  });
+
+  it('defaults widthUnit to px when missing', () => {
+    // Simulates a tableHeader node before Step 1 fix — no widthUnit attr at all
+    const node = { attrs: { colwidth: [100] } };
+    const tcPr = generateTableCellProperties(node);
+    const tcW = getTcW(tcPr);
+    // Should use pixelsToTwips (not inchesToTwips), producing 1500, not 144000
+    expect(tcW.attributes['w:w']).toBe(String(pixelsToTwips(100)));
+  });
+
+  it('preserves existing cellWidth when colwidth is null', () => {
+    const originalCellWidth = { value: 3000, type: 'dxa' };
+    const node = {
+      attrs: {
+        colwidth: null,
+        widthUnit: 'px',
+        tableCellProperties: { cellWidth: originalCellWidth },
+      },
+    };
+    const tcPr = generateTableCellProperties(node);
+    const tcW = getTcW(tcPr);
+    // Should preserve the original value, not write 0
+    expect(tcW.attributes['w:w']).toBe('3000');
+    expect(tcW.attributes['w:type']).toBe('dxa');
+  });
+
+  it('preserves existing cellWidth when colwidth is empty array', () => {
+    const originalCellWidth = { value: 3000, type: 'dxa' };
+    const node = {
+      attrs: {
+        colwidth: [],
+        widthUnit: 'px',
+        tableCellProperties: { cellWidth: originalCellWidth },
+      },
+    };
+    const tcPr = generateTableCellProperties(node);
+    const tcW = getTcW(tcPr);
+    expect(tcW.attributes['w:w']).toBe('3000');
+  });
+
+  it('filters non-finite values from colwidth', () => {
+    const node = { attrs: { colwidth: [100, NaN, 50], widthUnit: 'px' } };
+    const tcPr = generateTableCellProperties(node);
+    const tcW = getTcW(tcPr);
+    // Only 100 + 50 = 150 should be summed (NaN filtered out)
+    expect(tcW.attributes['w:w']).toBe(String(pixelsToTwips(150)));
+  });
+
+  it('preserves original cellWidth for pct width type', () => {
+    // Simulates a pct-imported cell: widthType is 'pct', colwidth is in pixels (from tblGrid fallback)
+    const originalCellWidth = { value: 5000, type: 'pct' };
+    const node = {
+      attrs: {
+        colwidth: [200],
+        widthUnit: 'px',
+        widthType: 'pct',
+        tableCellProperties: { cellWidth: originalCellWidth },
+      },
+    };
+    const tcPr = generateTableCellProperties(node);
+    const tcW = getTcW(tcPr);
+    // Should preserve original pct value, NOT rewrite with pixelsToTwips(200)
+    expect(tcW.attributes['w:w']).toBe('5000');
+    expect(tcW.attributes['w:type']).toBe('pct');
+  });
+
+  it('resolves widthType dxa from node attrs', () => {
+    const node = { attrs: { colwidth: [100], widthUnit: 'px', widthType: 'dxa' } };
+    const tcPr = generateTableCellProperties(node);
+    const tcW = getTcW(tcPr);
+    expect(tcW.attributes['w:type']).toBe('dxa');
+  });
+
+  it('falls through auto widthType to tableCellProperties.cellWidth.type', () => {
+    const node = {
+      attrs: {
+        colwidth: [100],
+        widthUnit: 'px',
+        widthType: 'auto',
+        tableCellProperties: { cellWidth: { value: 1500, type: 'dxa' } },
+      },
+    };
+    const tcPr = generateTableCellProperties(node);
+    const tcW = getTcW(tcPr);
+    // 'auto' is the uninformative default — should fall through to tableCellProperties type
+    expect(tcW.attributes['w:type']).toBe('dxa');
+  });
+
+  it('falls through auto widthType to dxa when no tableCellProperties type', () => {
+    const node = {
+      attrs: {
+        colwidth: [100],
+        widthUnit: 'px',
+        widthType: 'auto',
+      },
+    };
+    const tcPr = generateTableCellProperties(node);
+    const tcW = getTcW(tcPr);
+    expect(tcW.attributes['w:type']).toBe('dxa');
+  });
+});
diff --git a/packages/super-editor/src/extensions/table-header/table-header.js b/packages/super-editor/src/extensions/table-header/table-header.js
index 21730c3da0..ff903db95f 100644
--- a/packages/super-editor/src/extensions/table-header/table-header.js
+++ b/packages/super-editor/src/extensions/table-header/table-header.js
@@ -17,8 +17,14 @@ import { renderCellBorderStyle } from '../table-cell/helpers/renderCellBorderSty
  * @category Attributes
  * @property {number} [colspan=1] - Number of columns this header spans
  * @property {number} [rowspan=1] - Number of rows this header spans
- * @property {number[]} [colwidth] - Column widths array in pixels
+ * @property {number[]} [colwidth=[100]] - Column widths array in pixels
+ * @property {import('../table-cell/table-cell.js').CellBackground} [background] - Cell background color configuration
+ * @property {string} [verticalAlign] - Vertical content alignment (top, middle, bottom)
+ * @property {import('../table-cell/table-cell.js').CellMargins} [cellMargins] - Internal cell padding
  * @property {import('../table-cell/helpers/createCellBorders.js').CellBorders} [borders] - Cell border configuration
+ * @property {string} [widthType='auto'] @internal - Internal width type
+ * @property {string} [widthUnit='px'] @internal - Internal width unit
+ * @property {import('../table-cell/table-cell.js').TableCellProperties} [tableCellProperties] @internal - Raw OOXML cell properties
  */
 
 /**
@@ -54,7 +60,7 @@ export const TableHeader = Node.create({
       },
 
       colwidth: {
-        default: null,
+        default: [100],
         parseDOM: (element) => {
           const colwidth = element.getAttribute('data-colwidth');
           const value = colwidth ? colwidth.split(',').map((width) => parseInt(width, 10)) : null;
@@ -69,11 +75,62 @@ export const TableHeader = Node.create({
         },
       },
 
+      background: {
+        renderDOM({ background }) {
+          if (!background) return {};
+          // @ts-expect-error - background is known to be an object at runtime
+          const { color } = background || {};
+          const style = `background-color: ${color ? `#${color}` : 'transparent'}`;
+          return { style };
+        },
+      },
+
+      verticalAlign: {
+        renderDOM({ verticalAlign }) {
+          if (!verticalAlign) return {};
+          const style = `vertical-align: ${verticalAlign}`;
+          return { style };
+        },
+      },
+
+      cellMargins: {
+        renderDOM({ cellMargins, borders }) {
+          if (!cellMargins) return {};
+          const sides = ['top', 'right', 'bottom', 'left'];
+          const style = sides
+            .map((side) => {
+              const margin = cellMargins?.[side] ?? 0;
+              const border = borders?.[side];
+              const borderSize = border && border.val !== 'none' ? Math.ceil(border.size) : 0;
+
+              if (margin) return `padding-${side}: ${Math.max(0, margin - borderSize)}px;`;
+              return '';
+            })
+            .join(' ');
+          return { style };
+        },
+      },
+
       borders: {
         default: () => createCellBorders(),
         renderDOM: ({ borders }) => renderCellBorderStyle(borders),
       },
 
+      widthType: {
+        default: 'auto',
+        rendered: false,
+      },
+
+      widthUnit: {
+        default: 'px',
+        rendered: false,
+      },
+
+      tableCellProperties: {
+        default: null,
+        rendered: false,
+      },
+
       __placeholder: {
         default: null,
         parseDOM: (element) => {
diff --git a/packages/super-editor/src/extensions/table/table.test.js b/packages/super-editor/src/extensions/table/table.test.js
index ecbbe3e566..520f4f5f06 100644
--- a/packages/super-editor/src/extensions/table/table.test.js
+++ b/packages/super-editor/src/extensions/table/table.test.js
@@ -506,6 +506,71 @@ describe('Table commands', async () => {
     });
   });
 
+  describe('toggleHeaderRow preserves cell attributes (IT-550)', async () => {
+    beforeEach(async () => {
+      const { docx, media, mediaFiles, fonts } = cachedBlankDoc;
+      ({ editor } = initTestEditor({ content: docx, media, mediaFiles, fonts }));
+      ({ schema } = editor);
+
+      // Create a 2x2 table with explicit cell attributes
+      const CellType = schema.nodes.tableCell;
+      const RowType = schema.nodes.tableRow;
+      const TableType = schema.nodes.table;
+
+      const cellAttrs = {
+        colspan: 1,
+        rowspan: 1,
+        colwidth: [150],
+        widthUnit: 'px',
+        widthType: 'dxa',
+        background: { color: 'FF0000' },
+        tableCellProperties: { cellWidth: { value: 2250, type: 'dxa' } },
+      };
+
+      const makeCell = (text) => CellType.create(cellAttrs, schema.nodes.paragraph.create(null, schema.text(text)));
+
+      const row1 = RowType.create(null, [makeCell('A'), makeCell('B')]);
+      const row2 = RowType.create(null, [makeCell('C'), makeCell('D')]);
+      table = TableType.create(null, [row1, row2]);
+
+      const doc = schema.nodes.doc.create(null, [table]);
+      const nextState = EditorState.create({ schema, doc, plugins: editor.state.plugins });
+      editor.setState(nextState);
+    });
+
+    it('toggleHeaderRow preserves widthUnit, widthType, background, and tableCellProperties', async () => {
+      const tablePos = findTablePos(editor.state.doc);
+      expect(tablePos).not.toBeNull();
+
+      // Position cursor in first row
+      editor.commands.setTextSelection(tablePos + 3);
+
+      // Toggle first row to header
+      const didToggle = editor.commands.toggleHeaderRow();
+      expect(didToggle).toBe(true);
+
+      const updatedTable = editor.state.doc.nodeAt(tablePos);
+      const firstRow = updatedTable.child(0);
+
+      // First row cells should now be tableHeader type
+      firstRow.forEach((cell) => {
+        expect(cell.type.name).toBe('tableHeader');
+        // Critical attrs that were previously dropped
+        expect(cell.attrs.widthUnit).toBe('px');
+        expect(cell.attrs.widthType).toBe('dxa');
+        expect(cell.attrs.colwidth).toEqual([150]);
+        expect(cell.attrs.background).toEqual({ color: 'FF0000' });
+        expect(cell.attrs.tableCellProperties).toEqual({ cellWidth: { value: 2250, type: 'dxa' } });
+      });
+
+      // Second row should remain tableCell
+      const secondRow = updatedTable.child(1);
+      secondRow.forEach((cell) => {
+        expect(cell.type.name).toBe('tableCell');
+      });
+    });
+  });
+
   describe('deleteCellAndTableBorders', async () => {
     let table, tablePos;
 
diff --git a/packages/super-editor/src/tests/export/tableExporter.test.js b/packages/super-editor/src/tests/export/tableExporter.test.js
index 673ef6e231..2c2577b93c 100644
--- a/packages/super-editor/src/tests/export/tableExporter.test.js
+++ b/packages/super-editor/src/tests/export/tableExporter.test.js
@@ -1,5 +1,5 @@
 import { getExportedResult, getExportedResultWithDocContent } from './export-helpers/index.js';
-import { twipsToPixels } from '../../core/super-converter/helpers.js';
+import { twipsToPixels, pixelsToTwips } from '../../core/super-converter/helpers.js';
 
 describe('test table export', async () => {
   const fileName = 'table-merged-cells.docx';
@@ -153,4 +153,94 @@ describe('tableHeader export', () => {
 
     expect(cells.length).toBe(2);
   });
+
+  it('IT-550: tableHeader and tableCell emit identical w:tcW for same colwidth', async () => {
+    const expectedTwips = String(pixelsToTwips(100));
+    const tableWithHeaders = {
+      type: 'table',
+      attrs: {
+        grid: [{ col: 1500 }, { col: 1500 }],
+        tableProperties: {},
+      },
+      content: [
+        {
+          type: 'tableRow',
+          attrs: {},
+          content: [
+            {
+              type: 'tableHeader',
+              attrs: { colspan: 1, rowspan: 1, colwidth: [100], widthUnit: 'px' },
+              content: [
+                {
+                  type: 'paragraph',
+                  attrs: {},
+                  content: [{ type: 'run', content: [{ type: 'text', text: 'Header' }] }],
+                },
+              ],
+            },
+            {
+              type: 'tableHeader',
+              attrs: { colspan: 1, rowspan: 1, colwidth: [100], widthUnit: 'px' },
+              content: [
+                {
+                  type: 'paragraph',
+                  attrs: {},
+                  content: [{ type: 'run', content: [{ type: 'text', text: 'Header 2' }] }],
+                },
+              ],
+            },
+          ],
+        },
+        {
+          type: 'tableRow',
+          attrs: {},
+          content: [
+            {
+              type: 'tableCell',
+              attrs: { colspan: 1, rowspan: 1, colwidth: [100], widthUnit: 'px' },
+              content: [
+                {
+                  type: 'paragraph',
+                  attrs: {},
+                  content: [{ type: 'run', content: [{ type: 'text', text: 'Cell' }] }],
+                },
+              ],
+            },
+            {
+              type: 'tableCell',
+              attrs: { colspan: 1, rowspan: 1, colwidth: [100], widthUnit: 'px' },
+              content: [
+                {
+                  type: 'paragraph',
+                  attrs: {},
+                  content: [{ type: 'run', content: [{ type: 'text', text: 'Cell 2' }] }],
+                },
+              ],
+            },
+          ],
+        },
+      ],
+    };
+
+    const result = await getExportedResultWithDocContent([tableWithHeaders]);
+    const body = result.elements.find((el) => el.name === 'w:body');
+    const tbl = body.elements.find((el) => el.name === 'w:tbl');
+    const rows = tbl.elements.filter((el) => el.name === 'w:tr');
+
+    // Extract w:tcW from both header and body cells
+    const getTcW = (cell) => {
+      const tcPr = cell.elements.find((el) => el.name === 'w:tcPr');
+      return tcPr?.elements?.find((el) => el.name === 'w:tcW');
+    };
+
+    const headerCell = rows[0].elements.filter((el) => el.name === 'w:tc')[0];
+    const bodyCell = rows[1].elements.filter((el) => el.name === 'w:tc')[0];
+
+    const headerTcW = getTcW(headerCell);
+    const bodyTcW = getTcW(bodyCell);
+
+    // Assert exact expected value (1500 twips = pixelsToTwips(100))
+    expect(headerTcW.attributes['w:w']).toBe(expectedTwips);
+    expect(bodyTcW.attributes['w:w']).toBe(expectedTwips);
+  });
 });