Dip treated and pressure treated timber both protect wood from rot, moisture and insects, but they work in different ways. Dip treated timber is submerged in a preservative solution, creating a protective coating on the outer surface of the wood. Pressure treated timber, however, undergoes a more intensive process where preservatives are forced deep into the timber using hydraulic pressure. This deeper penetration provides stronger, longer-lasting protection, making pressure treated timber the more durable option for garden structures exposed to the elements.