A rug liner lets you change the warmth of a compatible turnout or stable rug as conditions change. Check the outer rugs fittings and cut before choosing how much fill to add.Start with the rug you already ownLook for the manufacturers liner attachment points. Swish clip-in liners connect at the withers with hook-and-loop tabs and at the back with two clips. Check that the fittings are present and match your liner. If the outer is a Swish wide-fit model, choose the corresponding wide-fit liner so the layers sit together correctly.For an outer rug without liner fittings, consider an independent layer such as the Swish 100g under-rug with surcingles. It fastens on the horse with its own chest fastenings and cross surcingles. Try it under your outer rug and check there is enough room for both layers to sit comfortably.Compare liner weights and cutsAdded fillStandard Swish fitSwish wide fit50g50g standard liner50g wide-fit liner100g100g standard liner100g wide-fit liner200g200g standard liner200g wide-fit liner300g300g standard linerStart with the smallest increase your horse needs. Adding a 50g liner to a 0g turnout gives a light layer beneath the waterproof outer. A 100g outer and 100g liner give a combined fill rating of 200g. Fit, fabrics, weather and your horses coat still affect how warm that combination feels. Use our horse rug weight guide to compare the options before going heavier.Check the fit with both layers onLay the two rugs together first. Check the liners tabs and clips reach their matching fittings and sit flat.Fit and fasten the layers using the manufacturers instructions. Check that the chest and shoulders have room to move and the withers are free from pressure.Watch the horse walk and lower its head. Check the layers stay in position and that straps lie smoothly without tangling or restricting movement.Check underneath after the horse has settled. If the coat is hot or damp with sweat, review the amount of fill. Lift or remove the rugs daily to check the horse and look for rubbing.For manufacturer specifications, see Swishs liner and under-rug range. The British Horse Society rugging guide covers fit and checking whether your horse needs a rug.