Here's from my stylist: "Porous hair is hair that has had the cuticle opened by overprocessing. It tends to be brittle and fragile and it absorbs water like a sponge and dries very slowly."
There is nothing that can heal it except to let the damaged hair grow out. However, certain products coat the hair and can help to create an artifical seal over the cuticle. I know that Fructis is a product line that uses these ingredients.
Hope this helps!