Seed Hay v Straw

I have a bale of hay which I think contains rather a lot of Straw. However I am told it is Seed Hay. Is Seed Hay hollow like Straw?

Parsnipbun recently posted something about straw but for the life of me i cant find post. I am sure someone will help!

Thanks. The supplier has told me it is Rye Grass and can be hollow inside.

Still like another opinion as it is identical to straw :?

Can you post a picture? Straw is basically the stalks from cereal crops, where as hay is grass. However, sometimes there is a bit of overlap. You get oat/wheat/barley hay which is cereal plants that have been cut early when they are still green and grass like, and grass that's been cut late when it's more mature and will have the thicker stems and more seed heads.