I'm going to use Theta-Solvent and Theta-temperature since that is what Wikipedia uses, and Wikipedia usually has the preferred names.
In order to get a polymer to the Theta-Condition two factors must be considered.
A Theta-Solvent is a poor solvent for a polymer is one such that the interactions between the polymer segments and the solvent are minimized. This results in polymer segment interactions to be maximized.
A good solvent for a polymer is one such that the interactions between the polymer segments and the solvent are maximized. This results in polymer segment interactions being minimized.
The Theta-temperature is the temperature for the particular theta-solvent
which minimizes interactions between the polymer segments and the solvent.
The combination of using a theta-solvent and being at the theta-temperature satisfies the theta-condition.
This makes experimental determination of important quantities such as the root mean square end-to-end distance or the radius of gyration much simpler.
This assumes that polymer will self-coil into its lowest energy configuration. For polymers with same unit repeating this is not unlikely.
For proteins in biological systems this self-arrangement is unlikely. Proteins do not have a "repeating unit." Therefore biological systems have a mechanism to fold a protein in a certain way.