Niger seed (nyjer seed or thistle seed) is known to be a favourite of finches, due to the shape and structure their beaks, which are suitable for a smaller type of bird seed.
“A quality product. The birds love it and eat the lot! I have tried cheaper brands, but a lot gets left in the container and goes mouldy. It doesn't happen with this one! Slightly more money, but worth it PLUS a donation goes to Cornwall Wildlife with every order, so win-win.”