Ageee,the OP gave no details.

The windows are vinyl insert replacement windows. They are Richardson's private label but made by midway windows. We live in upper Illinois.

Keep looking....................

I find it odd that this particular window only gets a .29 ufactor despite incorporating duralite.

Where are you located in the US as replacement window companies can be regional. The general names you want to look for are Okna, Sunrise, Polaris, Kensington and possibly a few others but many including these as I mention can be and are somewhat regional. I am generally a Marvin fan but you can do better, and a quality vinyl unit will be less expensive (or at least should be).

Quality vinyl will render the best performance, no doubt about it. Forget anything sold at the local building supply stores or home improvement centers, they are builders grade garbage.

the majority of high quality/ performance vinyl will be sold through dealers.