There are products currently on the market which are liquid applied vapor barriers which act as or outperform Tyvek.
However you should see evidence of the liquid applied film.
- First look for a coloration change in the wood sheathing. For example, one manufacture, STO, produces a liquid applied vapor barrier which is yellow in color and easy to spot.
- Secondly, to properly install a liquid vapor barrier, a mesh tape or screed should be applied over all seams in the exterior wall sheathing so that the liquid applied vapor barrier can properly seal the joints.
If you do not see any of these changes on the exterior of your home I would question the method and material used.
- Do not hesitate to request a specification sheet for the material installed by the contractor.
- If required you can also call upon your local building official inspecting the home during construction to assist you. They can request from the contractor an ICC/ES legacy report for the material installed.
This report will give the description of the material and its performance rating based on standardized test in the building industry. I f the contractor has been untruthful during the building process, I would carefully begin documenting items and instances of wrong doing so that you have a basis for termination of their contract.