Hello,

Thank you for posting in the Infragistics community !

Exporting group fields is not currently supported. To achieve this you would need a more custom approach, so I suggest you follow these:

1) In the button click event before you call .Export:

    public void Button1_Click(object sender, EventArgs e)
    {

        // 1. create a worksheet to export the grid to
        Infragistics.Documents.Excel.Workbook book = new Workbook();
        book.Worksheets.Add("Report");

        // 2. Define merged cells region, which will acts as the group field

        book.Worksheets[0].MergedCellsRegions.Add(0, 0, 0, 2); // 2 defines the number of cells to span
        book.Worksheets[0].MergedCellsRegions[0].Value = "Details"; // set value for the merged cell region, i.e the header text of the group field

        // 3. Rebind the grid with AutoGenerateColumns = True, or define new columns without utilizing groupfFeld

        this.WebDataGrid1.Columns.Clear();
        WebDataGrid1.DataSource = GetDataSource();
        this.WebDataGrid1.AutoGenerateColumns = true;
        this.WebDataGrid1.DataBind();

        // 4. Export the grid

        this.WebExcelExporter1.Export(this.WebDataGrid1, book.Worksheets["Report"], 1, 0); // 1 means export begins with 1 row offset from the top of the worksheet. This is     needed because the first row that is mergedcellsRegions is not part of the grid's rows
    }

2) Handle RowExported event.

When e.CurrentRowIndex == 1 (this is actualy the grid's header row) we copy its cells' format (font, style, background color) and set them to e.Worksheet.Rows[0], which is the mergedcells region row.

Please see the attached sample that demonstrates the suggested approach and let me know if it meets your requirements.