About Vinyl Records...
Vinyl LPs should be kept clean and stored vertically using light, even
pressure against the record and at room temperature (below 75 degrees F).
Direct sunlight, increases in temperature and/or uneven storage pressure are
the principal components that can lead to warping vinyl records.  If a record is
improperly stored and/or kept in a high-temperature environment, the vinyl
may warp and the record may become unplayable.

Warped vs Dished Records

A warped record reveals one or more “up and down” or bent areas in the
record surface that are easily observed as the record is spinning on the
turntable (viewed from the side of the record).  

A dished record is a record whose surface is curved from one side of the
record to the other.  There is a convex side (high center) and concave side
(low center).   On the turntable, the center of the concave side touches the
platter and the right and left edges of the record will be raised off of the
platter.  When the record is flipped over to the convex side, the center is
raised up the spindle and the edges will appear to evenly touch the platter.  
You can push down on the center of the convex side of the record to
momentarily flatten a dished record.   

Dished records are often the result of improper manufacturing but they can
also be repaired by the Vinyl Flat Record Flattener.

Record Weights and Chemical Composition

Vinyl LPs manufactured in the 1950s and 1960s were heavy and record
weights of 150 to 160 grams were common.  Records made in the 1970s and
1980s were considerably lighter and typically weigh around 110 to 130 grams.  
Some records made in the 1970s (notably, RCA’s DynaflexTM series) are as
light as 100 grams.  

Today, the trend has circled back to heavier records with most current
releases weighing between 150 and 180 grams and some records weighing
200 grams.

The chemical composition of records also varies.  A typical record is not
100% vinyl – additional chemicals are often added to save costs.

All of the above factors:  the type of surface problem (warp vs dish), the
weight of the record, and the chemical composition present an enormous
challenge to the record repair process.  However, the Vinyl Flat,
when used
properly, will repair practically any warped or dished record.