Excel provides a couple of settings that control this feature. First, Excel will let you you control saving of the thumbnail image when you first save your workbook or when you use the Save As command to save your workbook under a new name. The Save As dialog box contains a Save Thumbnail check box at the bottom.
Select the check box, and when you save your workbook the preview image is saved with it. The image represents the appearance of the first worksheet in your workbook. You do not have control over which worksheet is used in the preview.
On some systems, the Save Thumbail check box may be selected by default; on others not. Whether the check box is defaulted to selected or not selected, is controlled by a Properties setting.
Below is how you change that setting in Excel 2010 and Excel 2013:
- Display the File tab of your Ribbon.
- Be certain the Info option is selected at the left side of the dialog box.
- Click the Properties link near the right side of the dialog box and then click Advanced Properties to display the Properties dialog box for your workbook.
- Be certain the Summary tab is selected.
- Select Save Thumbnails for All Excel Documents check box at the bottom of the dialog box.
- Click on OK to close the Properties dialog box.
- Save your workbook.
Please note that the only way to save a thumbnail for an existing workbook that does not have one already saved, is to open the workbook and use the Save As dialog box (click F12 to display it) to re-save the workbook. (Do not forget to make sure the Save Thumbnail check box is selected before saving.)
It should also be noted that if you save your workbook via macro, there does not appear to be a way in VBA to set this, so macro-saved workbooks are not saved with a thumbnail, and the only way that I know of to save that thumbnail is to later open the workbook and manually go through the Save As steps to save it with the thumbnail.
If you still cannot see the thumbnails in a Windows Explorer window, make sure you have the view in that window set to use medium (or larger) icons. Any other views may not display the desired thumbnails.