Hi Mike,
 
Thank you for your question.
 
The mattresses in our Origins range are 13" deep and the majority of mattresses in our Artisan range are 12" in depth.  This is to allow for a quality spring system for support and a high GSM count of either Natural or Synthetic fillings which makes up the Upholstery (comfort) layers. 

 
It may be worth reading the article in the link 'here' which explains the basics of mattress construction. 
 
If you have any further questions please do not hesitate to contact the office on 0161 437 4419.
 
Kind regards,
Amy.