what is Sloper and what is block, both terms are confusing many fashion designers, and to clear the confusion with these terms, I will attempt to define both of them, because a sloper and a block are not the same. You may also want to search for terms like “sloper” and “block” to read further information.
A sewing sloper is also commonly called a sewing block, a pattern block, a foundation pattern, a basic, basic block, or any combination of the previous terms. Sloper – this term is used to define a pattern for any object which does not have seam allowance. You will be using it to describe a clothing pattern.
Block – this term is used to define a pattern for any object which has seam allowances and will be used repeatedly to create new patterns. Your bodice block may be the same as your bodice sloper with seam allowance added, however you can also have a jacket block which is an entire jacket pattern that you can use to create new jacket patterns by simply making small changes to the jacket block rather than drafting a jacket completely from scratch again. In industry the block is decided by which style sells well, this is why you can purchase an item from the same brand season after season which fits exactly the same way – they use the block that sold well and then make minor changes to style it differently for each season.
To summarize: In industry there will never be a jacket sloper because slopers are never actually used in pattern drafting once the very first pattern is made. And they are only used by designers or pattern drafters who do not have a set of blocks to work from already. As a pattern drafter becomes established in their career they will have already made a basic pattern for most items and will thus have blocks to start with. As a home sewer who is attempting to make their own patterns, you may use your own custom sloper often because pattern making without seam allowances is much easier for novice pattern makers and therefore home sewers and some dressmakers may have a jacket sloper (a pattern for a jacket without seam allowance). I was taught by a career dressmaker to not use seam allowances on patterns for example because we used hand basting stitches to mark the sewing lines on the fabric and just ensured to cut enough seam allowance to do whatever finish we were planning.
Be aware of using the terms correctly and educating people you know to use them correctly also. In addition, be aware of the information source you are using to be clear if they are using the terms correctly or not. Many home sewing “patternmakers” who have made books to sell to the home sewing market use the incorrect terms and this makes everything very confusing. If you are speaking with a professional industry patternmaker, or you attempt to get a pattern made for yourself, you could end up with difficulties in communication and/or errors in your pattern if you use the wrong terms (for instance if you call it a block when there is no seam allowance the pattern maker may not add seam allowance and then your garment is going to be quite small)