MDPE AND HDPE

High density PE is better than medium density PE.

Physical, chemical, thermal properties are all enhanced as the density goes up.

But, the one potential problem may be in low temperature performance and thermal expansion/contraction. As plastics cool they shrink faster than metals. (This is what doomed the space shuttle that exploded, O-rings act differently than coatings on metals but still shrink faster.)

You need to talk to a pipe supplier. Post the question on Global Spec.

BTW, typing in all caps means you are yelling.

Ah ha! Your question is Worded much clearer in the form of a question, But your still lacking the "?" mark.

Refer to the Data for both materials:

MDPE (Film Grade)

HDPE (pipe grade)

Couldn't find the properties for pipe grade MDPE Film grade was the closest i could get in under a minute. Those Data-sheets are only the overview for the entire family. If your looking for more specific information such as brands or variations of the material just utilize MATWEB.