This screw caps create a positive seal that protects against product escaping and prevents product contamination by outside substances. White Polypropylene screw cap provides clear surface for writing on cap. Poly Vinyl liner provides an excellent moisture barrier. One mil Poly Vinyl film bonded to one mil High Density Polyethylene on a number 30 white pulp paper backing. Superior to plain pulp paper because it provides an excellent moisture barrier. General purpose; suitable for wide range of applications. Chemical resistance; good for mild acids, alkalis, solvents, alcohols, oils and aqueous products. Poor for active hydrocarbons and bleaches. These screw caps are for use with sample vials or bottles. 83-400 Size. White. Polypropylene. Poly Vinyl/Pulp Liner. Wheaton #: 239421.