HTTP slow, but HTTPS fast.

Does anyone know how on earth can https be about 4 times faster than http on a web site?

This happens from the Internet and from other PCs on the same network, but is seems to be the same from the web server itself.

I'm using dsl and have a 4 port router and Dynamic NATP has to be enabled for the router to work at all. I guess it could be something to do with DNS. I have DNS Proxy enabled and DNS disabled on the router.

Thanks a million.

Hennie