Double Decker and Boost are both thick, filling Cadbury bars, but the way they build that bulk is completely different, one stacks two separate fillings, the other layers biscuit under caramel.
Two Cadbury bars, two very different structures
Both bars sit in the Cadbury range, but they were designed around different eating experiences. Double Decker launched in 1976 and is built as literally two decks, a crisped-cereal nougat layer on top of a softer chocolate-nougat base. Boost arrived nationally in 1985, built instead as a single biscuit base carrying a thick layer of caramel.
Layered nougat and cereal vs biscuit and caramel
- Double Decker — a crunchy cereal-studded nougat layer sits on a softer, denser nougat base, the two textures stacked rather than mixed, all coated in milk chocolate.
- Boost — a crisp biscuit layer runs the length of the bar under a thick, chewy caramel top, coated in milk chocolate. The crunch comes from the biscuit rather than any cereal pieces.
Nearly a decade apart
The gap between the two launches is part of why they feel so different: Double Decker was already established as Cadbury's answer to a multi-textured bar by the time Boost arrived, so Boost went a different route, leaning into the biscuit-and-caramel format that was proving popular elsewhere in the market rather than repeating the layered-nougat idea.
Which one to pick
If you like contrasting soft and crunchy layers in one bite, Double Decker delivers that directly. If you want a denser, more toffee-forward bar with a firm biscuit base, Boost is the one to grab.
Frequently asked questions
What is inside a Double Decker that makes it different from other Cadbury bars?
Double Decker has two distinct layers, a light nougat-and-crisped-cereal top layer sat on a separate chocolate-flavoured mousse-nougat base, all under a milk chocolate coating, giving it a genuinely two-textured bite.
What is the difference between Double Decker and Boost?
Double Decker's two layers are soft nougat and crunchy cereal pieces. Boost is built around a crunchy biscuit base with a thick caramel layer on top, making it denser and more toffee-forward than Double Decker.
When did Double Decker and Boost launch?
Double Decker launched in 1976. Boost followed almost a decade later, arriving nationally in 1985.