The bore is narrower, because the walls are thicker, but plastic can be run in longer lengths without coupling, and in slower bends, and the material is slipperier, so who really knows what the net difference is? I certainly haven't tested it.
With Speedfit it looks to me as though they would, because they're plastic, but the Hep2o stainless steel ones are very thin and feather into the pipe wall.
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