This technique will improve extension throughout your thoracic spine.

Start on your back with your knees bent. Place the foam roller under your mid back, support your head, keep your hips on the ground and extend over the foam roller. Take 3 deep breaths and then return to the start position. Move the roller to a new spot either higher or lower and extend again. Take 3 deep breaths. Repeat the extensions on 3-5 different spots along the mid back.