Clear,not silvered bags. But they're stored in a Stainless Steel locker. If you draw any vacuum, you need to freeze the water first or it absolutely will suck into the mechanism. I don't worry about drawing a vacuum. I just seal. Honestly, since the bags aren't pre-sterilized and since the vacuum won't really remove ALL of the air anyway, I don't worry about the air left in the bag when I seal it.