We install a 20 mil thick material throughout the entire crawlspace. We do not use thin plastic on the walls because we do not want to create a seam where the stem wall and the ground meet which is usually the wettest part of your crawlspace and a poor area to create a taped seam.
Our material is 20 mil thick from edge to edge.
Our competition will call their material 20 mil thick but they are measuring from the highest point on the material. It is actually 16 to 18 mil thick. It is a difference you can see.
Our competition will use a thinner plastic on the walls or clear plastic to save on material cost. Clear plastic is so thin bugs can eat right through it and it does not tape or seal well at all. Thinner plastic is weaker and less protective.
We at A Healthy Home, require a dehumidifier to be installed on every job. Why bother to encapsulate your crawlspace if you are not going to dry out the moisture that has entered over the years and then ensure that the proper humidity levels are maintained.
Our competitors will some times leave the dehumidifier out of the bid to come in lower then once they get the job suggest that a dehumidifier might be a good idea. This is deception. It either proves they are unethical or that they do not understand the basic principles of how to protect a home from moisture.
Our competitors will say "we seal it so tight you don't need a dehumidifier" If you seal water in a plastic bag will it ever dry out? No. And neither will the moisture that is already in your crawlspace.
So you must circulate dry air. A dehumidifier is the only way to do this once all sources of moisture entering the crawlspace have been sealed.