A woman's sack back and petticoat of yellow watered silk brocaded with a design in silver thread of vertical leafy and undulating trails, and with detached butterflies and flower baskets and floral sprigs on the ground. The sack back is open at the front with pleated robings to the waist and elbow-length sleeves with double, scalloped and pinked sleeve ruffles. The bodice and sleeves are lined with linen, with a bone on either side of the back. The back has two double box pleats, stitched at the neckline and carefully arranged to show the undulating trails in the silk pattern. There is a waist seam from front to side back seam, with the skirts pleated at the seam. There are no pocket openings. The sack back is made of 4 widths of silk with a partial panel on each side of the front, folded back in an angled pleat running from hem to waist. The skirts are lined with yellow glazed wool and the hem faced with yellow linen tape.
The petticoat is made of 2 widths of silk and would have been worn apron-style. There is a box pleat at the centre front and flat pleats on either side. The waist is bound with yellow linen tape which froms ties to fasten. The petticoat is decorated with two dentelated, pinked and scalloped flounces, arranged horizontally. It is lined with a thin grey-brown watered silk.
Both sack back and petticoat are very carefully pieced and clearly made over from an earlier incarnation; areas of fading at the petticoat waist suggest possible for a furnishing. The linen tape tie at the the centre back waist of the bodice lining and those on the bodice fronts were probably added for fancy dress in the late 19th century.