Literally though the dow and the spectrapure membranes look identical, same color l, design just with a different sticker on them.
Spectrapure membranes are in fact Dow Filmtec membranes. Dow Filmtec membranes have a rejection rate range between 96% to 99%. See the data sheet.
I believe Spectrapure batch tests these Dow membranes and and selects the ones that actually have a 99% rejection rate and markets them as their SpectraSelect 99% rejection rate membranes. They also claim to treat them with some sort of proprietary process, but I know nothing about that!