The Irwin 5 lb. blue chalk is used for creating chalk lines on both floors and walls. The 5 lb packaging is ideal for the user who are required to create chalk lines on a regular basis. IRWIN STRAIT-LINE marking chalks have a newly engineered flip-top cap that keeps the chalk in the bottle where you want it and keeps it from spilling out where you do not want it. The flip-top cap, available on all IRWIN STRAIT-LINE chalk bottles, seals the chalk in an airtight chamber, keeping out moisture and reducing the risk of clumping.Interior or exterior use High visibility chalk for self chalking line reels For use on a variety of surfaces including wood, drywall, concrete, stone, and metal Chalk containers are filled by weight, not volume Marks are temporary Provides great visibility