Inner sleeve
An inner sleeve is a thin sleeve sized to fit a standard card snugly that goes inside a standard card sleeve, a layering BCW calls double-sleeving.
In more detail
BCW's Regular Inner Sleeves measure 64 by 89 millimeters and hold one standard 2 1/2 by 3 1/2 inch card in a snug fit. They are acid-free polypropylene, and BCW designs them to sit inside a standard outer sleeve.
BCW says its own Standard Card Sleeves are made for single sleeving but can be paired with inner sleeves for double-sleeving. Ultra PRO sells inner sleeves called PRO-Fit Inner Sleeves, made from 50 micron film, against 45 microns for its penny sleeves.
BCW describes its inner sleeves as durable enough for frequent handling. For a card you plan to send to a grader, follow the company's packing instructions instead: CGC asks for each card in a sleeve and then a semi-rigid holder, and TAG asks for each card in a soft sleeve, then in a semi-rigid card shield.
Related terms
Where Rip.fan covers it
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