Abstract: Sheets and sheet kits for use in protecting openings in a walled structure are provided. The sheets are generally plastic sheets having at least one corrugated region and a pair of lateral corrugated regions. The corrugated region and the lateral corrugated regions are configured such that the sheet can resist a missile weighing about 9.4 lbs (4.3 kgs), having a cross-sectional impact area of about 5.25 in2 (34 cm2), and impacting the sheet at a velocity of about 50 ft/s (15.24 m/s). The sheet kits include mounting tracks. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that is will not be used to interpret or limit the scope or meaning of the claims. 37 CFR 1.72(b).