Silvacore is created on a German-made machine imported to the UK. Only two brands are made on this beautifully-engineered machine and one of the two brands is Silvacore (the other is Duraflue). "I have Silvacore in my chimney" (Julian Patrick, author of The Stovefitter's Manual).
A flue liner is not a product you want to fail within just a few years. Silvacore is designed for professional trade-fitters desiring a premium product for chimney lining.
Silvacore chimney liner is created from TWO compressed stainless-steel layers and this unique laminate stays smooth when the product is passed around chimney bends (with a lesser-quality liner the laminate usually comes apart when dragged through bends - allowing acids from soot deposits to enter and later cause corrosion).
904 and 316 are grades of stainless steel. If you are a heavy user of coal/smokeless fuel then one would be advised to ensure that, as a minimum, the inside layer of your liner is 904 grade.