We use the Gaussian-fit results of Paper I to investigate the properties of interstellar HI in the Solar neighborhood .
The Warm and Cold Neutral Media ( WNM and CNM ) are physically distinct components .
The CNM spin temperature histogram peaks at about 40 K ; its median , weighted by column density , is 70 K .

About 60 \% of all HI is WNM ; there is no discernable change in this fraction at z = 0 .
At z = 0 , we derive a volume filling fraction of about 0.50 for the WNM ; this value is very rough .
The upper-limit WNM temperatures determined from line width range upward from \sim 500 K ; a minimum of about 48 \% of the WNM lies in the thermally unstable region 500 to 5000 K. The WNM is a prominent constituent of the interstellar medium and its properties depend on many factors , requiring global models that include all relevant energy sources , of which there are many .

We use Principal Components Analysis , together with a form of least squares fitting that accounts for errors in both the independent and dependent parameters , to discuss the relationships among the four CNM Gaussian parameters .
The spin temperature T _ { s } and column density N ( HI ) are , approximately , the two most important eigenvectors ; as such , they are sufficient , convenient , and physically meaningful primary parameters for describing CNM clouds .
The Mach number of internal macroscopic motions for CNM clouds is typically about 3 so that they are strongly supersonic , but there are wide variations .
We discuss the historical \tau _ { 0 } - T _ { s } relationship in some detail and show that it has little physical meaning .

We discuss CNM morphology using the CNM pressure known from UV stellar absorption lines .
Knowing the pressure allows us to show that CNM structures can not be isotropic but instead are sheetlike , with length-to-thickness aspect ratios ranging up to about 280 .
We present large-scale maps of two regions where CNM lies in very large “ blobby sheets ” .

We test the McKee/Ostriker model of the interstellar medium by explicitly modeling our data with CNM cores contained in WNM envelopes .
This modeling scheme works quite well for many sources and also predicts the WNM filling factor reasonably well .
However , it has several deficiencies .