Rug fitting and sizing can be a complex thing and varies from horse to horse and different rug brands. Our Eurohunter rugs tend to be fairly true to size and fit most horses from light frames to heavy frames.
With a winter rug it is okay for it to be a bit looser to allow the horse to move about and a good synthetic rug will have surcingle straps around the belly for added support. Some problems with shoulders rubbing can be related to the rug fit and it is always good to check the type of rug you are using fits around the shoulders and through the body. A synthetic rug generally rubs less than a canvas rug.
A summer rug is a rug designed to keep your horse clean and cool during the hotter months of the year and needs to fit correctly to be comfortable and functional for the horse. It is usually a case of you get what you pay for. The rug needs to be strong enough to withstand daily life in the paddock by light enough to not be too hot.