I think it is subfloor/plywood/underlayment/flooring.
Here is what it says
UNDERLAYMENTS FOR SOLID BAMBOO
Depending on the application, our flooring can be installed (nailed, glued or *floating) over an approved underlayment to meet the needs of customers, building specifiers and condominium associations desiring greater thermal insulation and sound isolation qualities. Note that when using an approved underlayment, pad or cushion there can always be slight movement, deflection or friction, squeaks or floor noise with any application. Floor noise is normal, to be expected and will vary from one installation type to the next or related to sub-floor type, flatness, deflection, and or related to the type of flooring material, species, the fasteners, relative humidity and the amount of topside pressure applied to the flooring. Therefore for these reasons floor noise is not considered a product or manufacturer defect.
White Silicon Vapor Shield®,
15 lb felt paper do not overlap seems under pre-finished flooring
Black asphalt saturated Kraft paper overlap seams 2” to 4”
Bellawood Platinum, install (film side up) Flooring minimum (≥3/8”thickness)
Bellawood Premium, install (film side up) Flooring minimum (≥3/8”thickness)
Eco Silent Sound, install (film side down) Flooring minimum (≥3/8”thickness)
Dream Home Insulayment, install (smooth side up) Flooring minimum (≥3/8”thickness)
Dream Home Cork (3mm), install (smooth side up) Flooring minimum (≥3/8”thickness)
Do not use plastic poly-sheeting over wood subfloors, wood components need to breathe