The strictest definition of a sloper is any pattern without seam allowance. That means a pattern for anything from a car seat cover to a diaper bag is a sloper if it does not have seam allowance. That said, the meaning of sloper has become corrupted. Most people use the word sloper to refer to a basic fitting shell. A basic fitting shell is only a sloper if it does not have seam allowance.
Now, the reason why I said “most people” is because this term is most often used by enthusiasts, sewing books, pattern books, sewing magazines, colleges, schools et cetera. The one place the word sloper is never used, is in factories and design departments. In other words, the very places people think the term is most often used is the one place where it is not. This is for several reasons.
First, in real life, patterns are not made without seam allowance. Only in extremely rare cases. Now, I can understand why you’d think making patterns without allowances is common because that’s the way books tell you to do it. However, the reason why books teach you to make patterns using slopers is because it is difficult -to say nothing of redundant- to continually illustrate the moves by first instructing you to subtract the seam allowance, do the instruction and then re-add the allowance. With books, it is much easier to start from nett and add seams after the fact. Now, just because books show you this way for the sake of instructional expediency, doesn’t mean we do this in real life. The best thing to do is to learn pattern manipulation skills from patterns that already have seam allowance. It’s a more advanced skill but you need to learn it that way because you’ll rarely make patterns any other way.
Another thing about misusing the definition of sloper to refer to a fitting shell is that it can be slightly insulting to non apparel makers because only 45% of the “apparel industry” is about making clothes. Most of the industry is sewn products, not clothing, and the term sloper is not exclusive to apparel production so if you use the term referring to clothes, you’ve slighted more than half the business because the real definition applies to everyone in the business because everyone has patterns. It may surprise you to know that sewn products people can be a little resentful that apparel people think they “own” the industry when it is sewn products people holding up more than half the sky.
By the way, sloper is one word you can safely delete from your working vocabulary because it marks you as a nube and if you’re working with catty people, they may snicker (as my own humiliating experience would testify). We don’t use patterns without seam allowance and we don’t use basic fitting shells so there’s no practical reason you’d need the word anyway. Yes, I know it sounds like spiffy official apparel industry lingo so you may hesitate to set it aside when you’ve heard it used by everybody else you admire and you think it makes you look like an insider whiz but it doesn’t have that affect. Trust me. By the way, if you don’t know these sorts of basic outsider missteps, do buy my book. Otherwise, you may have toilet paper stuck to the heel of your Manolo Blahnik’s and never know why nobody takes you seriously in spite of your having the wherewithal to fork out two thousand dollars for your shoes (or $60,000 for your education). Before you know it, we’ll have you chatting in plain english, just like everybody else :). Before I forget, “croquis” is another safe deletion from your vocabulary. That’s in the book too.
Now, if you came to this entry on slopers because you are interested in more information about fitting shells, see these entries:
Drafting and Anthropometry
On reviewing pattern books (a review and how to select a pattern book)
On drafting and The European Cut
Muslin, “muslins” & protos
What is a Block? (a sloper is not a block either).