📏 PERFECTLY SIZED: 1000 #3 glassine envelopes 2 ½ x 4 ¼” 63.5 x 108mm. ✅ ARCHIVAL-QUALITY GLASSINE: These acid free archival envelopes are made of high quality glassine. glassines are made of a PH neutral, semitransparent paper with no harmful chemicals.