Sewing - Drysack

drysack

Features:

Dual layers of waterproof-breathable fabric, with wrong sides facing, protects waterproof-breathable membrane from abrasion.
Dual layers have no common seams other than at opening, so likelihood of water penetrating is negligible, unless sack is cut somehow.
Because fabric is waterproof-breathable, moisture which penetrates first layer and gets trapped between layers can easily evaporate.
Closure by folding top of sack. Sufficient for rain which leaks into top of backpack and flows down, or for rain blowing into tarp at night and falling on drysack, though not for submersion.
Water vapor flows through waterproof breathable fabrics depending on temperature gradient. Since electronics do not generate heat when powered off, moisture can seep into drysack as condensed water vapor. However, modern smartphones and associated electronics usually water resistant, so small amounts of moisture will not cause damage.
Final weight depends on fabric. If 3 oz/sqyd 2-layer Goretex Paclite with polyester ripstop face fabric from therainshed.com, final weight of 70 grams.

Materials:

Instructions:

Cut two pieces of fabric 13" x 40".
Fold fabric so that it is 13" x 20" and sew together on long sides with 1/4" seam. Repeat for other piece of fabric.
Seal seams. Allow to dry. Dust with talc or corn starch so sealer will not stick to itself when sacks inserted inside one another.
Turn one sack inside out and insert inside other sack. Sew together at top. Fold over twice to make 3/8" hem.