Premium Mattress Topper vs mattress encasement super king size new: which is safer?

Where these two actually differ

• We flag Volatile Organic Compounds (VOC) off-gassing from polyurethane foam, Polyester cover degradation and microfiber shedding, Polyurethane foam degradation and chemical leaching with age and Water-resistant coating composition (undisclosed) on the Helix and not on the Nectar.
• We flag Water-resistant chemical composition (undisclosed), Polyurethane backing degradation, Microplastics shedding from synthetic fibers and Flame retardant interaction (if mattress underneath uses legacy treatments) on the Nectar and not on the Helix.
• The Helix is polyurethane foam, polyester cover where the Nectar is Polyester/polyurethane encasement with water-resistant treatment, which is most of the difference in these two grades.
• The gap is 45 points, wide enough that this is not a close call, and the Helix is the one to buy.
• We are less certain about the Nectar grade, at 42% confidence against 72%, because it discloses less.