Ideas on mesh to keep substrate separated

long story short, a tank I am going to be scaping soon but I use two different types of substrates / additives for a planted tank, in the past I have had problems with the bottom layer becoming mixed with the top layer and it just looks ugly and not ideal

I thought of using some kind of mesh, has anyone used any of this before and any ideas on what kind of mesh would be safe under water

Do the roots have to penetrate it? If not, have you considered the plastic mesh like we use to make dividers for betta tanks? It can be found in craft sections at stores. Comes in different colors.

I suppose you might try plastic needlepoint mesh and/or nylon window screen as both would hold up underwater. Stainless steel mesh might also be an option. However, I'm not sure about plant roots as they would penetrate but if/when you went to replant, pulling them up could be a problem w/o root damage.
Having 'said' the above, I've been happy with just [somewhat] coarse sand alone. I'm using pool filter sand and Byron has had great results with big box store play sand (Sacrete I believe). I'm not sure I see any advantage in media layers requiring separation.

Interesting thought with the roots, the products I am using / have spare around the house are ADA PowerSand special and ADA Amazonia, the PowerSand special contrary to its name is not sand but rocks and some soil mixed together plus other products. It’s placed at the very bottom on the glass usually only A few mm thick, and topped of wth the normal Substrate, this is what I’m trying to keep at bay and kinda stay at the bottom..

I have asked the company I bought it from the question do the roots need to be in contact my presumption is no as it’s on the very bottom and not very thick, but it’s just a presumption.

The plastic mesh you use for separating beta tanks what is that called I’m I intreagued to look it up

shadecloth or plastic flywire. If you want green and soft then mosquito netting from a shop that sells sewing machines and material for making clothes.

Here’s a pic of the plastic canvas that I use for dividers in my beta tanks.. It’s called Darice canvas. You can get it on EBay. In the States, I get it at Walmart.

Just checked, it’s also available on Amazon. Good luck!