In 1.7, thatch would block light fully (which had the original function of creating dark, cool rooms for storage) and would block rainfall.

The original light opacity of thatch was 255. This is up for debate if light level no longer affects decay etc.

Thatch doesn't block rainfall currently because of its Material.PLANTS definition; it will need a material for which blocksMovement returns true, such as what it used in 1.7, Material.GRASS. However, Material.GRASS is also isSolid, killing grass underneath it; if this is not intended, a new material will have to be created.