Can't make htaccess work for subdomain

Recently I removed some content from my main site to a subdomain.

What I am seeking to do in simple terms

Redirect http://www.domain.com/foldername/*.* TO http://subdomain.domain.com/foldername/*

For this in the htaccess file I tried using:

Redirect /foldername http://subdomain.domain.com/foldername/

This is not working because the server is creating a loop for http://subdomain.domain.com/foldername/ as well.

How should this be changed? I haven't the faintest clue.