I am trying to take out our old curtains and replace with the Bunnings roller blinds but have come across this straw stuff. Does anyone know what it is
Looks like horsehair plaster. Common in houses up to around the 50s on straight walls, later on curved walls. Basically plaster before gyprock sheeting was used. Normally literally plaster strengthened by animal (normally horse) hair.
Welcome to the Bunnings Workshop community @hello9819. It's great to have you join us and many thanks for your question.
I see you have already received some helpful advice from the very knowledgable @JDE. I'd agree that it is horsehair plaster and it's quite common. I would like to add that whenever dealing with older sheeting products, which you are not definitively sure of what they are constructed from, I would advise treating them as Asbestos. Make sure you dampen the surface when drilling and sanding, wear appropriate PPE gear and clean up the area after work is done. It's better to be safe than sorry.
The house I am renting in at the moment also has the same horsehair sheeting boards and a lot of the plaster was falling off the walls when I moved in. I've repaired all of the exposed horsehairs by patching it with plaster and painting. I didn't do this because I was worried about it necessarily being Asbestos but more-so that it was unsightly.
Please let us know if you needed further advice or had any questions.
I'd agree with @JDE it looks like horse hair plaster. I live in an old QLDer and we had to replace a few walls and that looks almost exactly the same as the stuff we ripped out.