Substrate screen mash

[kueluck]

I used two layers of fiberglass screening. Your spingtails most likely won't go below your top substrate anyway unless it dries out. Springtails are going to seek out moisture and then food.

[Louis Charles Bruckner]

Agreed.
I have used fine window screen from a local hardware store, just make sure it is made from fiberglass (better because it doesn't rot or get brittle over time like plastic or vinyl)

I also like screen material because I can cut it to form and stitch together pieces to make it form fitting to odd shapes in false bottom vivairums.
I.E around potted plants or water features.