This made me curious. I checked the tags that came on my Helium (bought 3/2004). It has Pertex Quantum for both the shell and liner.
The Helium EQ came out shortly after I bought this bag.
On Marmot’s website, I see that the EQ features Pertex Quantum N-090 Ripstop with Endurance for the shell and Pertex Quantum N-090 Taffeta for the lining. Probably more important for the weight gain is that the EQ features a full length zipper rather than the 1/2 length zipper of the Helium.