Creating a Duct Tape Sloper to Improve Fit (Part 1/2 – Duct Tape Sloper Series)

Disclaimer: I’m not a professional sewist or pattern maker. This tutorial simply describes an approach I find helpful in improving the fit of my sewn garments.

I started sewing a couple of years ago, and after a frustrating beginning in the wonderful world of fitting issues, I discovered the fabulous Curvy Tutorials on CSC. Who knew there were adjustments for shoulders, busts, waists and tummies?? And since when was grading between sizes allowed when all of my Kwik Sew patterns shouted at me in capital letters not to do it?!?

More significantly I realised that, like me, many women don’t fit clothing patterns straight from the packet. Being able to grade between different sizes and make fit adjustments is one of the key joys of sewing. Unfortunately, it can also be baffling, time consuming, sometimes unsuccessful, not to mention that every time you try a new pattern, you have to start all over again.

A big step forward for me has been making my own sloper, and then comparing my sloper with flat pattern pieces to make better informed decisions about sizing, grading, and adjustments.

This approach was inspired by a range of articles I read online. It combines a few different ideas and I’ve found it invaluable to help me understand the following concepts:

• How my individual body shape translates to a flat shape, which I can compare to flat pattern pieces.
• How I need to adjust a flat pattern to improve the fit of the finished garment.
• Why some styles work better for my curves, and why I struggle to fit some styles no matter how many muslins I make.

What is a sloper?

A sloper (also known as a “block”) is the basic bodice, skirt, or pants shape that clothing patterns are based on. To create unique clothing patterns, the following are added to a basic sloper:

• Pattern ease: To make a garment wearable when you move around.
• Design ease: To give the garment its unique shape.
• Design features: Such as seam lines, darts and fastenings.

Pattern companies generally use standard measurements in their slopers. Seamwork Magazine has a great article on The Origins of Clothing Sizes.

The CSC has an informative article on Buying and Using a Sloper.

The rest of this post details the approach that I use to make my own sloper, based on a cast of myself I create using duct tape.

Making your own sloper using duct tape

Important information: You can’t create your own cast by yourself using duct tape. You need to find someone you trust to help you make your cast, draw on the critical details, and carefully cut you out of the cast.

I use a variation on this Quick and Easy Duct-Tape Dress Form tutorial from Threads Magazine to make a cast of myself using duct tape. This article is for making a dress form. Since I want to make slopers for separates, I make separate casts for a bodice, pants, and skirt.

You’ll need the following supplies:

• “Sacrificial” under-layer: Such as cling film, a jersey t-shirt or bike pants – this needs to be tight fitting and fit to your natural curves.
• Duct tape: Perforated duct tape is much easier to use.
• For tracing: Transparent interfacing, tracing paper or grease proof paper.
• Scissors with rounded tips (NOT pointy tips).
• Permanent marker to draw on tracing material and duct tape: For drawing on black duct tape, I found metallic marker pens worked well.

Duct tape sloper supplies

Use the following basic procedure to create your sloper:

1. Make a cast of yourself.
2. Draw the details that you want to record on the duct tape.
3. Cut off your cast.
4. Translate your cast into your sloper.
5. Check the fit with a muslin.
6. Store your cast for future use.

Step 1: Make a cast of yourself

Making a cast of yourself is really simple. All you need to do is wear some great underwear, put on the sacrificial under-layer which the duct tape will be stuck on to, and then get someone you trust to cover the sacrificial under-layer in little pieces of duct tape. The duct tape needs to sit flat on you with zero ease to give the most accurate cast.

For the under-layer, I found plastic cling film gave the best results, although it was transparent for the person putting the tape on for me (thanks Mum!).  The jersey t-shirt or bike pants shrank away from the duct tape overnight, causing sticky problems later.

The Threads article suggests using three layers of tape. If you’re after a flat sloper, not a solid 3D dress form, one layer of duct tape is enough.

The taping process is a bit time consuming so be patient. Shorter pieces of tape better capture the details of your curves. Any significant movement during the taping process (bending, walking) can displace the tape and reduce the overall quality of the cast.

Don’t make your cast when the weather is hot; you’ll warm up inside the duct tape really fast, especially if you use cling film for the under-layer.

Getting started applying duct tape to cling film for a bodice sloper. (Massive thanks to my anonymous friend for letting me use this picture.

Step 2: Draw the details that you want to record on the duct tape.

Using a permanent marker, get your helper to draw the following details on your duct tape cast while you’re still wearing it. These details are really helpful for comparing your finished sloper to an actual pattern piece:

• Vertical lines: Centre front line, centre back line, side seam lines
• Horizontal lines: Under-bust, waist, and fullest part of hips
• Shoulder seam lines (where the front and back bodice meet): Shoulder hinge point (where you generally want your sleeves to attach to your bodice).
• Bust apex: Yes, it’s awkward but really helpful for bust and waist dart placement, and as a reference point for FBAs later.
• Dart lines: Where you want to place your bust dart and any front or back waist darts.

Some tips about where to draw dart lines:

• Generally, bust darts start 1 – 2 inches to the outside of the bust apex and slope down to the side seam.
• Front waist darts are aligned under the bust apex.
• Front waist darts in bodices start 2 – 3 inches below the bust apex and may be a fish eye shape (stopping before the hip line) or continue to the hem for a flatter fit.
• Back waist darts are aligned under the shoulder blades.
• Back waist darts in bodices start 3 – 4 inches below the shoulder blades (about the underbust line).

Here is a bodice cast with the details drawn on the duct tape. You can see the drawings for the vertical centre front seam; horizontal under-bust, waist and full hip lines, waist darts, horizontal hip line; and X for bust apex.

Here is a skirt cast with the details drawn on the duct tape. You can see the drawings for the vertical centre front seam, waist darts, horizontal hip line, and X for belly button – which is a proxy waist reference.

Step 3: Cut off your cast

Ask your helper to cut off your cast using your rounded tip scissors and cutting along vertical seam lines. For bodice casts, I cut along the centre back seam. For pants and skirts, I cut along a side seam.

Cut through the under-layer along with the duct tape. Be careful not to cut through underwear or skin. I cut from bottom to top and gently lift the cast off the skin as I go. This is much easier with rounded tip scissors, rather than pointy tip scissors.

Scissor tips:

• Shorter scissors can go over curves more easily than longer scissors.
• Blunt scissors can be dangerous if you need to put too much force behind them.

Step 4: Translate your cast into your sloper

Separate the front and back pieces of each side by cutting along the side seams and shoulder seams, if you’re making a bodice sloper.

Cut along any dart lines and smooth the cast pieces so that they are lying as flat as possible.

L to R: Front bodice cast with armhole dart, bust dart and waist dart; Back bodice cast with fish eye dart.

Because many pattern pieces are meant to be placed on the fold, you’ll end up with a sloper from each side of your cast which gives you more dart options for comparing with flat pattern pieces later.

For my bodice cast, I cut:

• One front piece with a bust dart.
• One front piece with a bust dart, armhole dart and a waist dart.
• One back piece with a fish eye dart under the shoulder blade.

For my pants/skirt cast, I cut:

• One front piece with a waist dart.
• One front piece with no dart – since my waist is not much smaller than my hips.
• One back piece with a waist dart.
• One back piece with a princess seam.

If your waist is small compared to your hips, you can choose to cut two waist darts in one of your front pieces and one of your back pieces.

Trace the cast pieces onto the transparent interfacing or paper. Draw on the darts and the horizontal lines: Underbust, waist, and fullest part of hips.

Cut out your traced pieces. These are your slopers!

Note: If you made a two-dart front bodice sloper, you can also use this to create a front bodice sloper with princess seams using this tutorial.

L to R: A front bodice sloper with a bust dart; a front bodice sloper with a bust dart and a full length waist dart; a back bodice sloper with a fish eye dart. Underbust and waist lines are marked on each sloper. Bust apex is marked on front slopers.

Step 5: Check the fit with a muslin

You can check the fit of your sloper and the location of your darts by making a muslin. The muslin can also be a good reference to see if your measurements have changed over time and you need to make new slopers.

When you cut out the muslin using your sloper, remember to add seam allowances to the side seams and any shoulder seams.

So you can get into the muslin, you’ll also need to add some pattern ease to these seam lines. For my muslins made from a poly-cotton poplin, I found 3/8 inch horizontal ease on the side seams and 1 inch vertical ease on any shoulder seams was enough to allow me to try on the muslin and get a good idea of its fit. If you don’t want any horizontal ease you could insert a zip in a side seam.

To construct the muslin, simply baste the side seams – and one shoulder seam if you’re trying a bodice sloper. You can pin the other shoulder seam closed once you’ve got the bodice muslin over your head.

When I tried on my bodice muslin, I decided to lower the bust apex and bust darts 1 inch. I re-drew my front bodice slopers with this alteration.

Step 6: Store your cast for future use

Store your cast pieces in a safe place so you can use them again to create more slopers with different design features. You can also cut them up to make your own pattern variations.

Next time in Part 2 – Using your own sloper with flat pattern pieces, I’ll talk about comparing your sloper with flat pattern pieces and using your sloper to make pattern alterations.