We do not make sails with a completely straight side because this would compromise the optimum tension on the central part of the sail. However, bear in mind that our "Made in Italy" sails (i.e. all "Saill" and "Solaria" models) have a concavity of 2% of the length of the side. So a 5 metres side, for example, has a maximum concavity (at the centre of the side) of 10cm.