The ergonomic design and materials used to make pads also changed through the 1980s to today. With earlier materials not being as absorbent and effective, and early pads being up to two centimetres thick, leaks were a major problem. Some variations introduced were quilting of the lining, adding "wings" and reducing the thickness of the pad by utilising products such as sphagnum and polyacrylate superabsorbent gels derived from petroleum. The materials used to manufacture most pads are derived from the petroleum industry and forestry. The absorbent core, made from chlorine bleached wood pulp, could be reduced to make slimmer products with the addition of polyacrylate gels which sucks up the liquid quickly and holds it in a suspension under pressure. The remaining materials are mostly derived from the petroleum industry, the cover stock used is polypropylene non woven, with the leakproof barrier made from polyethylene film.