$this->fields_list['name'] = array(
    'title' => $this->l('Name'),
    'filter_key' => 'b!name'
);

$this->fields_list['attributes'] = array(
    'title' => $this->l('Attributes'),
    'callback' => 'getAttr',
    'filter_key' => 'b!id_product'
);

public static function getQuantities($echo, $tr)

public static function getAttr($id_product)
{
    $attributes_combinations = Product::getAttributesInformationsByProduct($id_product);
    if (is_array($attributes_combinations) && count($attributes_combinations))
    {
        $tmp = '';
        foreach ($attributes_combinations as $ac)
            $tmp .= $ac['group'] . ': ' . $ac['attribute'] . '<br />';
        return $tmp;
    }
    return '-';
}