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Arcsin Undies - Arccos Undies Mod Pack - Downloadable PDF Sewing Pattern


This is a downloadable PDF Sewing Pattern.

NOTE: This pattern is an Arccos Undies Mod Pack and requires pattern pieces and instructions from the Arccos Undies Pattern

Finally, you say, there is underwear with a working fly front!! Where have these been all our lives!! Everyone has been waiting for these!! 

GARMENT SPECIFICS The Arcsin Undies are a modification of the Arccos Undies: it has the same hipster cut, featuring a very cute overlapped fly front. The crotch is fully lined, and uses a great trick to enclose all the seams.

This garment can be entirely constructed with a sewing machine, serger optional. Techniques required include zig zag stitches and working with elastic.

SUGGESTED FABRICS Knit fabrics with 50-75% stretch, preferably with a spandex content. Bamboo, Rayon, or blends with Cotton, Lycra, Silk, Spandex, Nylon, Tencel. 100% cotton tends to stretch out quickly. Measure stretch by marking out 4” of fabric, then gently stretch to max.


  • All sizes 1/2 yard


  • All sizes 1.5 yd Waistband elastic 
  • All sizes 2.5 yds Leg band elastic 
  • All sizes 8 inches Accent Elastic

SIZES This pattern includes sizes XXS-000/00 to 3X-24/26 PLEASE NOTE: The Arccos Undies (required for this pattern) are currently only graded between XS-0 to 2X-20/22. We plan to bring early patterns up to date in 2022. 

Sophie’s waist is 25”, her hips are 35.5”, and she is 5’10” tall. She is wearing size XS - 0/2 with no modifications.

sophie hines underwear size chart

 Pattern download link will be emailed to you after checkout. It will arrive in a ZIP file format. Simply click to unzip, and print at 100% without scaling. You can download the pattern up to three (3) times, so make sure you download it on your personal computer and keep it filed in a safe place!

You may not sell garments made using this pattern. 


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