When are single layer ESD mats adequate?

[jusaca]

From what I read in the past ESD mats for workbenches should typically consist of two layers:
- A top layer, which is static dissipative (in the MOhm range), to slowly and safely dissipate any charge on components or PCBs
- A bottom layer, which is in the conductive region (kOhm range), to ensure an equally good connection of all parts of the top layer
In our lab we have these double layer mats basically everywhere.

But there are also single layer mats like this one from RS Components: https://us.rs-online.com/product/rs-pro/7873114/71005298/

As far as I can see these single layer mats all are completely in the conductive range and are therefore not safe to handle ESDS components on. A charged component would possibly discharge to fast when touching the mat.

So, wher are these mats used? In which cases are they adequate?

[thm_w]

https://assets.rs-online.com/v1699883904/Datasheets/2810785848a1f4be51026c1ff91ad2da.pdf

You can put a 1MOhm resistor on the grounding point if you are worried about that.

[jusaca]

Well, this is what we do with every ESD mat.
But a single layer mat still enables quite a large capacitive discharge (wether there is a 1 MOhm at the outlet or not). So the protection is not really given.
At least when I understand the difference between these single layer and double layer mats correctly. If my understanding is wrong, feel free to explain.

[jusaca]

Is this just a stupid question of me and nobody knows how to respond to it?
Or is this a tricky topic and answers might not be so easy or clear?

[thm_w]

Its not a stupid question.
There are some standards for ESD protection you can read about here: https://www.gotopac.com/art-esd-iso-standards-s20-20
I don't see any mention of minimum resistances, only maximums.

They cover the case you ask about:

Some examples of ESD damage are:

    A charged object or person comes into contact with an ESDS item.
    A charged ESDS device makes contact with another conductive object at a different potential (including a ground).
    While exposed to an electrostatic field, an ESDS item becomes grounded.

This is why handling and transporting ESDS items inside and outside an EPA will require the use of static protective enclosures made of materials that vary depending on the situation and the destination of the items. Inside an EPA, minor discharge materials, as well as static dissipative materials, can provide adequate protection. Outside of an EPA, the use of low static charge and discharge shielding materials is recommended. These materials are not discussed in this document, but it is important to recognize their different applications. For more clarification on these materials, you can consult the ANSI/ESD S541.

Often companies can decide if they want to follow these standards to the letter or not.