Is the iPhone 4 Back Panel an OEM part?

I bought the back panel for the iPhone 4 via iFixIt. When it arrived I noticed two things:

1) The replacement part is lighter than the original (significantly)..

2) It does not slide in/out as easy as the original...

Is this an OEM part or just a facsimile? I was under the impression that the extra price was because this is an Apple OEM part.

Part Number: IF182-00201

Thanks...