PVAD : This gum looks like PVA except a greenish tint has been added to make it more visible to the naked eye. According to some people the tint has disappeared on some of the later printings, but they have been assured that it is still technically a gum called dextrin.
S.A (Acrylic): Introduced before layflat but sold only in the Tyne Tees television area and philatelic counters. The first issues were withdrawn from sale because the ink used to cancel them would not adhere to the shiny surface.
Sold originally in booklets of 20, the stamps were smaller in size and of a horizontal format, the head size was reduced in size accordingly.
PVA (Layflat): This is still a PVA gum but has layflat qualities, the latest (except for acrylic) to be used by the Royal Mail. Recently introduced to stop the paper from curling in humid conditions. It looks creamy in colour, slightly darker darker than PVA or Dex and less shiny in appearance. Two types exist, the creamy type and a whiter version. It is believed that the whiter version is the same gum but with a thinner variation of paper. This was first tested on the 19p & 25P values issued in 1995.