If you have a duvet cover you love, please feel free to insert the entire KAILU raw silk duvet — cover and all — into your duvet cover at home. Having two covers will add extra protection, and should not impact breathability. Our raw silk duvets work as a system: there are ties on both the raw silk cores and duvet covers so everything lines up and fits perfectly. We do not allow new customers to buy raw silk cores separately.  We do allow repeat customers to buy additional raw silk cores if they wish to switch from a single core duvet to a dual core duvet. Please email lili@kailusilk.com if you're a returning customer who wishes to do this. Please note: additional shipping costs and sales taxes will apply.