The Native serialization format uses a very simple algorithm that enables SQL Server to store an efficient representation of the UDT on disk. Types marked for Native serialization can only have value types (structs in Microsoft Visual C# and structures in Microsoft Visual Basic .NET) as members. Members of reference types (such as classes in Visual C# and Visual Basic), either user-defined or those existing in the framework (such as string), are not supported.

The serialization format is unknown.

The UserDefined serialization format gives the developer full control over the binary format through the Microsoft.SqlServer.Server.IBinarySerialize.Write and Microsoft.SqlServer.Server.IBinarySerialize.Read methods.