A US patent issued having a "summary of invention" NOT covering the claims (e.g. describing different materials).
Is it valid?
A "summary of the invention" section is not a hard requirement of a patent application. During prosecution claims get amended and in a follow-on application the claims might be directed to some aspect that is covered but not focused on in the initial application. The specification is usually not amended in order to avoid a concern over introducing "new matter" so the claims and the summary end up out of sync. The more important issue is whether the application as filed, as a whole, suficently supports the claims.
On the other hand, if a summary sections says "my invention is a ", some judges will use that to further narrow their interpretation of the claims to a . That is one reason some people are leaving off summary sections altogether.