The A2 is the go-to sail on most boat. Sprit boats never run dead down wind because the asymmetrical spinnaker gets blanketed behind the main sail if they sail below 155 degrees AWA. For an asymmetric spinnaker flown off of a centerline pole, “running” is when the boat sails with the apparent wind angle greater than 90 degrees until the boat is sailing as deep as 155 degrees AWA. An A2 (light/medium runner) is used in apparent wind speeds of 8-18 knots. To sail help sail as low as possible, UK Sailmakers designs these sails to be full-sized with a full entry and a high clew so that the middle of the sail will flatten out and rotate to windward of the headstay to get as much of the sail as possible out of the wind shadow of the mainsail.
The heart of faster spinnakers is the construction method. The panel layout UK Sailmakers uses is called Matrix, which is a full radial layout that features narrow panels, each oriented to better align the threads in the cloth with the primary loadpaths in the spinnaker. This is the most effective way to reduce distortion and make the strongest sail for its weight.