Does your foam need to be replaced?
Since there are different qualities of foam, there is not a specific length of time that can be used as a guide.  Foam is expensive.  
Depending on the size, the foam insert can cost more than a custom made cover.  A good quality foam will last, so you should not have
to buy the foam insert again for 12-20+ years.  Therefore, as your tastes change, you will only have to change the fabric when it comes
time to decorate again.    

If the cushion is still comfortable to you then you can probably wait.  Remember that the foam can be changed at any time, so if the
foam has a few more years of life, than you can simply buy a new piece of foam in a few years.  However, if it is beginning to have a
"rounded" front edge, become powdery, or if the seat foam doesn't offer you the support that you need to feel comfortable then you are
probably ready for new foam.

See our indoor foam web page for what to look for when purchasing foam, and if you would like to know even more about foam and its
properties, there is a very good article published in "
In Touch" magazine's July 1994 issue.
Foam
The foam cushion in the picture on the left is wrapped in dacron.  Dacron
helps give the cushion a nice crown when the cushion is not in use, but does
not provide any additional support.  Dacron is recommended, because it
helps protect the fabric from wear against the foam, and from mildew if
anything is spilled on the cushion.  If something is spilled on the cushion and
is absorbed into the foam, the dacron does not hold liquid, so it maintains a
dry area between the damp foam and the fabric.  This will allow the fabric
remain dry, and help prevent mildew on the fabric.
The cushion below is a mockbox cushion, and the polyester wrap help
soften the edges of the foam.
AD Specialty Sewing  & Upholstery
(847) 639-0390  /  info@grovesofa.com
410 Northwest Highway, Fox River Grove, IL. 60021