Both use Harrison Spinks' Cortec™ Quad pocket spring technology, natural upholstery and seasonal sleeping surfaces. They are also available in the same principal tension choices. The main differences are found in their additional spring layers, natural filling blends and finishing details.

Does a higher spring count make the Caspian better?

Not necessarily. Mattress spring counts can be misleading when viewed on their own because the headline figure includes different types and sizes of springs positioned throughout the mattress.

The Caspian combines its main Cortec™ Quad spring system with dual layers of HD 3000 and HD 2500 micro-springs, alongside Posturfil pocket springs. The Ruby uses Cortec™ Quad springs alongside HD 2500 micro springs and a layer of Posturfil pocket springs.

This means the difference between 12,500 and 13,750 shouldn't simply be interpreted as the Caspian having 1,250 additional conventional mattress springs. The two mattresses use different supplementary spring arrangements, which may influence how their comfort layers respond and feel.

Spring count is only one part of choosing a mattress. Its tension, upholstery, construction and how it feels when you lie on it are equally important.

How do the natural fillings compare?

Both mattresses make extensive use of natural fibres, although their upholstery blends aren't exactly the same.

The Ruby layers a British wool and viscose blend with a British wool, hemp and flax blend, and a cotton, hemp and flax blend. The Caspian layers a British wool and viscose blend with a British wool and hemp blend, and a cotton and flax blend, with its Ortho version adding a further layer of home-grown hemp for extra support.

Both draw on natural fibres grown and processed by Harrison Spinks on their own Yorkshire farm, so the sustainability credentials are closely matched, even though the specific blend proportions differ.

Are the two mattresses built the same way?

Construction-wise, they're very similar. Both feature three rows of hand side stitching for edge support and a 25cm border, and both are Seasonal Turn mattresses with a warming wool side for winter and a cooling cotton side for summer.

Both are also available in the same core range of tensions – Gentle, Medium and Firm – with a dedicated Ortho option for those wanting a firmer, more supportive feel.

What's the price difference?

In kingsize, the Ruby 12,500 is priced at £1,739, while the Caspian 13,750 typically retails from around £1,949, depending on retailer. For an £210 saving, the Ruby gives up one supplementary micro-spring layer (HD 3000) and a slightly different natural filling blend – while matching the Caspian on tension range, stitching, seasonal turn construction and Harrison Spinks' 10-year guarantee.

For most sleepers, the practical difference between the two will be subtle. The Caspian's additional spring layer may suit those who prefer a touch more contouring support, while the Ruby offers very similar comfort and construction at a lower price point.