New Treated Brown Hardwood Sleepers are either Alder, Aspen or Birch. These sleepers have more consistent edges and less splitting than oak sleepers. Pressure Treated Brown. 2.4m x 100mm x 200mm. Can be used with timber-fast screws, mending plates and corner braces. New Hardwood Sleepers are machined from natural, unseasoned timber that has not undergone any drying process, so they will naturally season over time. This means the timber may distort or split as it dries and shrinks in different directions. This is completely normal and helps to give sleepers a natural look. It will not affect the integrity of the product if orientated appropriately. Shade of brown can vary between batches, from light brown, red-brown to dark brown.