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Difference in sound: PS material is relatively hard, so the sound of knocking sounds crisper. The PP material has good strength but not enough hardness, so the sound is dull.

Difference in appearance: PS can be very transparent, while PP has the most transparent appearance, but it is still mushy, like frosted glass. 

The difference in outline: PP has good tension, while PS is relatively rigid. In terms of hand feel, PP is softer than PS. In general, for pp and ps products with the same thickness, the transparency ps>pp, the hardness ps>pp, and the tension pp>ps.