How to determine if a SQL Server backup is compressed?

Compressed SQL Server backups can be verified in PowerShell using a handy PowerShell function. This comes in handy when you need to verify if existing SQL Server backups are compressed.

The following PowerShell function returns 1 when a SQL Server backup is compressed. You need to provide the (remote) database server and backup file location.

Param
(
  [string]$Server,
  [string]$BAKFile
)

[Void][System.Reflection.Assembly]::LoadWithPartialName('Microsoft.SQLServer.SMO')
[Void][System.Reflection.Assembly]::LoadWithPartialName('Microsoft.SQLServer.SMOExtended')

$SMOServer = New-Object Microsoft.SqlServer.Management.Smo.Server $Server
$Res = New-Object Microsoft.SqlServer.Management.Smo.Restore

$Res.Devices.AddDevice($BAKFile, [Microsoft.SqlServer.Management.Smo.DeviceType]::File)
$Res.ReadBackupHeader($SMOServer).Rows[0].Compressed

Provide server hostname ($Server) and backup file ($BackFile), usage:

PS C:\Users\janreilink> .\Desktop\IsBackupCompressed.ps1 localhost D:\mssql\backups\testdb.bak
1

Source: JNK on Database Administrators StackExchange. There is also an Stored Procedure available by Max Vernon to determine if a database backup file is initialized for compression.