Can I use free proxies with curl safely

Can I be sure my communication won't be readable connecting to https websites through free proxies using curl like that:

$curl=curl_init();

curl_setopt($curl, CURLOPT_CAPATH, $mycapath);
curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, 1);
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, TRUE);
curl_setopt($curl, CURLOPT_POST, 1);
curl_setopt($curl, CURLOPT_POSTFIELDS, "private=data");
curl_setopt($curl, CURLOPT_URL, $sslurl); 

$response = curl_exec($curl);