Our polyester “L” seals are sealed on one short and one long side. The .004 thickness offers extra rigidity and support for heavy or fragile documents. They are made of inert, acid-free polyester and are a popular choice for preservation of photos, negatives, letters, documents, drawings, and many other flat items. “L”-seals construction is particularly good for delicate or brittle items as the enclosure opens easily, allowing gentle insertion of the artifact. The size listed is the size which will fit inside the envelopes; they are slightly larger externally. Packages of 10.