Hot dip galvanization involves immersing the pipe in a molten zinc bath, creating a thick and durable coating that provides excellent corrosion resistance. On the other hand, pre galvanized pipes are coated with a layer of zinc through a different process, resulting in a thinner coating. While both options offer protection against rust and corrosion, hot dip galvanized pipes are generally more robust and long-lasting. So, if you're looking for maximum durability and longevity for your greenhouse, hot dip galvanized pipes are the way to go.