How can I perform a case-insensitive filter on a JTable?

rowSorter.setStringConverter(new TableStringConverter() {
    @Override
    public String toString(TableModel model, int row, int column) {
        return model.getValueAt(row, column).toString().toLowerCase();
    }
});
rowSorter.setRowFilter(RowFilter.regexFilter(jtfFilter.getText().toLowerCase()));

Add the standard regex case-insensitivity flag:

rowSorter.setRowFilter(RowFilter.regexFilter("(?i)" + text));

I've tested this with your SSCCE (thanks for providing that) and it works.