In the Australian timber industry, "H6" refers to a specific strength classification for treated softwood timber products. H6 timber has been treated with preservatives to protect it from decay and insect damage and is typically used for applications that require a high level of durability, such as in marine environments or for construction in ground contact.

According to Australian standards, H6 timber has a minimum structural strength of F27, which means it has a bending stress capacity of 27 megapascals (MPa). This makes it a strong and durable option for construction projects that require long-lasting timber products.

H6 is for outside, structural, in contact with salt water, such as boardwalks, piers and jetties.