using NPOI.SS.UserModel;
using NPOI.HSSF.UserModel;

following are the codes -

// Create a new workbook
var workbook = new HSSFWorkbook();

var headerLabelCellStyle = workbook.CreateCellStyle();
headerLabelCellStyle.Alignment = HorizontalAlignment.CENTER;
headerLabelCellStyle.BorderBottom = CellBorderType.THIN;
var headerLabelFont = workbook.CreateFont();
headerLabelFont.Boldweight = (short)FontBoldWeight.BOLD;
headerLabelCellStyle.SetFont(headerLabelFont);

var sheet = workbook.CreateSheet("Bids");
var rowProject = sheet.CreateRow(1);
var cell4 = rowProject.CreateCell(0);
cell4.SetCellValue("Project Name");
var rowCom = sheet.CreateRow(2);
var cell5 = rowCom.CreateCell(0);
cell5.SetCellValue("Bid");
var rowEst = sheet.CreateRow(3);
var cell6 = rowEst.CreateCell(0);
cell6.SetCellValue("Date");

//Auto-size each column
for (var j = 0; j < sheet.GetRow(5).LastCellNum; j++)
{
// Bump up with auto-sized column width to account for bold headers
sheet.SetColumnWidth(j, sheet.GetColumnWidth(j) + 2100);
}
// Save the Excel spreadsheet to a MemoryStream and return it to the client
using (var exportData = new MemoryStream())
{
workbook.Write(exportData);
//string saveAsFileName = string.Format("Bids.xls");
Response.ContentType = "application/vnd.ms-excel";
Response.AddHeader("Content-Disposition", string.Format("attachment;filename={0}", "Bids.xls"));
Response.Clear();
Response.BinaryWrite(exportData.GetBuffer());
Response.End();
}