products.php

<?php

$combination = new Combination($id_attribute);

$attributes = array();
$attributes_str = '';
if (Validate::isLoadedObject($combination)) {
    $attributes_names = $combination->getAttributesName(Context::getContext()->language->id);
    if (is_array($attributes_names)) {
        foreach ($attributes_names as $attributes_name) {
            $attributes[] = $attributes_name['name'];
        }
    }
    $attributes_str = implode('-', $attributes);
}

$attribute = $id_product.'-'.$attributes_str;