Key points about Johnnie Walker Select Casks:
Experimental nature:
This series is considered an opportunity for Johnnie Walker's master blender to experiment with different cask finishes, creating unique expressions beyond their standard range. 
Rye Cask Finish:
The most popular Select Cask variant, featuring a finish in ex-rye whiskey barrels, giving the whisky a spicier character with notes of cinnamon, nutmeg, and vanilla. 
American palate appeal:
The Rye Cask Finish is often described as being crafted with the American whiskey drinker in mind, due to its rye spice profile. 
Limited edition:
Select Casks are typically released as limited editions, meaning they may not always be readily available.