The bag arrived with brown spots along the zipper. I washed the topper on delicate, and once I pulled it out to line dry, I noticed there were small brown flecks all over the fabric. I tried dusting them off and they smeared into the fabric!! I don’t know what it was, but it didn’t make me feel very clean. 
I probably won’t be adding this to my bed until I wash it again and see if the mysterious brown specks come off.