Change the UL for WooCommerce product loop start and end if your are not using a list, but for example Twitter Bootstrap. There are two other ways of doing this, overwriting the WooCommerce template files or using your own templates files. See https://github.com/woothemes/woocommerce/issues/5197.

gistfile1.txt

// Change the UL for WooCommerce product loop start and end if your are not using a list, but for example Twitter Bootstrap. See https://gist.github.com/Willem-Siebe/2f2f64012b9cfe36df1a.

function woocommerce_product_loop_start() { 
	echo '<div class="wsis-wc-product-loop">'; 
}

function woocommerce_product_loop_end() { 
	echo '</div>'; 
}

you shouldn't really overwrite the template files.
To be exact, you can actually change the loop start and loop end by copying the files: wp-content/plugins/woocommerce/templates/loop/loop-start.php into your themes folder -> wp-content/themes/mysuperchildtheme/woocommerce/loop/