People list or talk about outer sleeve thickness in different measurements. This is an example of how people might mix up the thickness of a sleeve
2 mil = 0.05 mm = 0.002 inch = 200 gauge
Common thickness are:1 mil, 2 mil, 3 mil, 4 mil, 5 mil
Common materials used:
Polyethylene know as PE, comes in different forms. Most inner sleeves and economical outer sleeves are made of LDPE and HDPE. These grades have excellent chemical resistance, meaning they are not attacked by strong acids or strong bases, and are resistant to gentle oxidants and reducing agents. PE can become brittle when exposed to sunlight, hence turning grey or yellow. Generally made from recycled material, unless stated otherwise.HDPE will typically have anti-static additives.
Mylar or BoPET (biaxially-oriented polyethylene terephthalate) is a polyester film. It has similar properties to BOPP and generally competes against each other. These harder films will become brittle over time and their seams will slowly fail.
Polypropylene know as PP, comes in different forms. Typically BOPP (OPP also fails into this category) or CPP are used to manufacture higher end outer sleeves due to their low haze and high clarity. The physical difference between the two is that BOPP tends to be made of very thin film and have a "cracking" noise when pinched, where CPP is used in thicker films and have the stretch properties of PE. BOPP will easily crack and rip (fail) when "hinged" repeatedly. BOPP is typically used as packaging film, like candies.. CPP has a price advantage over Mylar (polyester) and BOPP.
Why use CPP for outer sleeves?
Environmentally inert. 100% recyclable.
Acid free. Contains no PVC.
Excellent optics. Highly reflective.
Moderate WVTR (water vapor transmission rate) barrier against moisture and odours.
Highly resistance to acids, alkaline, grease and oil. Exceptional resistance to corrosive chemicals. Exceptional toughness, wear and abrasion resistance.
Natural living hinge properties, Folds won’t easily crack or crinkle.
Passes the P. A. T. test for no photographic enclosure reactivity. Used for archival purposes., such as photographs.
- Why store my records outside of their album sleeve?
- Some will say that it helps to reduce ring wear...some will say that it will eliminate seam splits...some like not touching the album sleeve for preservation...some think it will minimize exposure to humidity...etc....
The simple answer is preference. For me, and others that have a collection of value (in my case over $10,000) or for an appreciation of the artwork, e.g. Black Sabbath's Greatest Hits features the "Triumph of Death" and it was drawn by Pieter Bruegel the Elder in 1562. You want the clarity to see the artwork and not the haze of an economical sleeve, but also the protection.
I have always viewed inner and outer sleeves as an insurance policy. If I'm spending $20 to $50 on a record, why wouldn't I spend another $1 to protect it? I have albums that I bought in the mid 1970's that look brand new and sound as though they were pressed yesterday. I also have album sleeves that were ruined due to inferior outer sleeves (PVC) leeching into the cardboard or not preventing moisture transfer due to humidity. It also reduces the amount of cleaning I need to do, as the I'm not sliding a record into an album jacket and creating microscopic dust.
I hope everyone finds this info helpful?