Download Zip In Memory And Extract File To Disk

I am trying to programitally download a file from a https server, that uses cookies (and hence I'm using httpwebrequest). I'm debug printing the capacity of the streams to check, but the output [raw] files look different. Have tried other encoding to no avail.

Code:
Sub downloadzip(strURL As String, strDestDir As String)
Dim request As HttpWebRequest
Dim response As HttpWebResponse
request = Net.HttpWebRequest.Create(strURL)
request.UserAgent = strUserAgent
[Code].....

So I get the right size file downloaded, but dotnetzip does not recognise it, and the files that get copied out are incomplete/invalid zips.