Glass and acrylic removable beds are just hand cut to size(custom=printer type), from scraps pieces. Typical window glass is around 3mm,, but any thickness will work,, you just have to make the proper Z-height adjustment, manually to the bed, which will mean having to re-level it,(just once), OR add a custom height spacer to hit the Home-Z-stop switch earlier. ( it all depends on which type of printer it is )
Acrylic was for unheated beds for PLA printing. 1/4" thickness is typical up to 200x200mm, but I use 1/2" for larger beds, up to 400x400mm. Glass works too, but if there are bed height adjustment screws sticking up higher than the bed,, you may lose a little build area.
Glass for heated beds takes a few more minutes to heat up, than the initial bed-temp reading,, so allow for that.
Removable beds can also be placed in the freezer for a few minutes, to make removal of your print item completely effortless.(it will almost just fall off the plate)
Also,, #4) PVA filament. Used in dual-extruders, with PLA as a water soluble support material. (not for bed adhesion,, just a fun fact )