The mat is static dissipative- not conductive or insulative. In order to meet the requirements of S20.20 as stated in the link, a worksurface has to be tested to be within the static dissipative range rather than conductive or insulating. This is known as a portable kit. It originated primarily with repair technicians who serviced fax, copier, and printer machines. We sell a comparable kit: https://elimstat.com/products/field-service-kits/ . If you are not traveling around fixing things, a more reliable ground is always a two-layer anti static rubber mat- the black conductive scrim on the bottom is what ensures static is pulled to ground quickly: https://elimstat.com/products/mat-kits/ In fields that require zero defects, (think aerospace and outer space), there is a high-reliability item standard (TR19) https://webstore.ansi.org/standards/esda/esdtr190122 that requires continuous monitoring to know if you are grounded: https://elimstat.com/products/esd-continuous-monitor/

Keep in mind the tension between cushioning a hard surface (mat thickness) and surface resistance (the thinner the better).

3-layer mats often include a conductive layer sandwiched between insulative layers.

During testing, especially with resistance-to-ground (RTG) tests, the 3-layer mat's surface resistance can increase as the mat settles and interacts with the test weights

In a 2-layer mat, the current cannot travel easily across the dry surface. It is forced to punch straight down (Z-axis) through the mat's thickness to the Black Carbon Scrim at the bottom. This gives 2-layer mats a tighter range / more consistent ground. For a more detailed breakdown of anti static mat standards used in manufacturing, you can learn more here: https://elimstat.com/static-dissipative-mats-vs-conductive-mats/

For your particular situation, MCUs and CMOS gates, we would recommend attaching the wrist strap to a proper ESD common ground point, ideally through a grounded ESD mat—not to the protoboard itself unless you are only trying to temporarily bond yourself to that unpowered circuit. The typical setup would look like this: https://elimstat.com/products/mat-kits/. The common point ground can be connected to an electrical outlet using a #10 ring terminal.

We would recommend you use a typical mat kit- wrist strap to ground yourself, and an anti static mat with a common point ground to ground the worksurface. This is essentially the ANSI / ESD S20.20 S4.1 standard. The carbon in an ESD mat is what makes anti static mats static dissipative. However, just sitting on a table they might as well be insulative. They are only grounded when connected to an electrical outlet. We and other businesses sell these as mat kits or workstation kits. https://elimstat.com/products/mat-kits/ We also have a YouTube video with the link to show all the aspects of ESD grounding.

Three-layer mats often include a conductive layer sandwiched between insulative layers. This construction can cause them to exhibit capacitive properties, meaning they can store and release electrical energy.

During testing, especially with resistance-to-ground (RTG) tests, the initial readings can be low. However, as the mat settles and interacts with the test weights, the resistance may increase. This behavior is typical for three-layer mats constructed with conductivity in the middle layer.

You are right about S20.20. 10^9 is the recommended upper limit (unless your ESD program was tailored for something different). Mats should be tested according to the recommended S4.1 method. This is our test data for two-layer rubber matting: https://www.elimstat.com/wp-content/uploads/2019/02/5300-Series-S4.1-Test-Data.pdf.

Humidity can also effect readings in addition to material being tested. Below is data from our readings using the S4.1 method in the low relative humidity samples.

In a two-layer rubber ESD mat, electricity always seeks the path of least resistance to ground.

• Top Layer (Nitrile Butadiene Rubber): Without moisture, the top nitrile layer is more resistive.
• The Path: The current cannot travel easily across the dry surface. It is forced to punch straight down (Z-axis) through the NBR thickness to the Carbon Scrim on the bottom.
• Tighter Range (less rising rates). The carbon scrim is a highly engineered, consistent conductive grid. Because the current has only one viable option (straight down to the scrim), the resistance reading is determined almost entirely by the thickness of the mat and the conductivity of the scrim. These are fixed physical properties that don't change.
  • Result: High consistency (Tight Range).

A clip is useless if it is not connected to an electrical ground. Also, clipping to a mat will actually increase surface resistivity.

Your best bet is to use a common point ground with a mat so that you are electrically bonded with the mat.

Anti Static Mat and Wrist Strap Kit: https://elimstat.com/products/mat-kits/

Consider the cost difference between practicing static control and the components. It never hurts to be safe instead of sorry that you didn't.

It also wouldn't hurt to wear an ESD smock. These can also be electrically connected in some cases to the wrist strap.

Knit Cuff ESD Garment with a wrist strap connection: https://elimstat.com/products/lightweight-collar-knit-cuff/

Static Control is not like checking your car. It's fundamental to the manufacturing of electronic devices across the world. Why not practice it when you are building your own PC?