I went into the access panel for my bathtub today. I was taking a look in prep for removing the tub. The only thing the panel granted immediate access to was the water pipes, behind which there was an insulation I'm not familiar with.

It was paper backed, which was dry and tore when I touched it. it was filled with a sort of sawdust that crumbled out. The paper seemed to be sweating salt-like crystals... looked like salt stains on the paper.

Any idea what kind of insulation this would be, or tips on how to remove it without creating a horrible mess would be appreciated. My house was built around 1970.

Thanks.