Consider using a pvc or oilcloth fabric for the outside to make the bag easier to wipe down
1Cut a piece of fabric measuring 35 x 30cm, then do the same with the matt vinyl. Lay the vinyl onto the wrong side of the fabric and cover with a tea towel. Iron on a medium setting for 8-10 minutes until bonded. Fold in half lengthways and draw diagonal lines on each side, starting 4cm in from the top cut edges and ending at the same side bottom corners.
2Cut away these two triangles. With fabric facing right side up, line up the zip with the edge of one short end, right side up. Open the zipper and pin in place. Thread the machine with black thread and use a zipper foot attachment to sew in place. Take the other top edge and line it up with the other side of the zip, right sides together. Pin and stitch into place.
3Switch to your standard sewing-machine foot and thread with white cotton. Sew down one side with a 1cm seam allowance and repeat on the other side. To make the bottom gusset, open up the point into a triangle and draw a line perpendicular to the seam measuring 5cm across. Stitch along the line and repeat on the other side. Snip off both points and turn right side out.