Sewing - Backpack

backpack finished

TBC strap attachment sized for 1.5" hip strap. Hip strap later reduced to 1" because only used to keep pack from falling overhead, not to bear weight. So strap attachment should be resized smaller.

Further discussion of backpack here.

Features:

Closed cell foam pad must be used to provide stiffness and padding. Closed cell foam pad can serve dual purpose as sleep pad at night and yoga exercise mat in morning. Pack sized for foam pad 20" x 71" x .5" (such as XPE foam from Seattle Fabrics).
Pack designed for bulky synthetic quilt. Down quilt/bag also acceptable, if bulky enough to keep bottom half of pack tightly stuffed. Otherwise, contents of pack will sag and pack will carry poorly.
User assumption: (a) torso length 18.5" (lowermost cervical vertebra to top of iliac crest); (b) neck circumference 15.5" (measured at middle of neck); (c) waist 32". If actual neck circumference significantly larger than assumption, then shoulder straps may cut into neck.
Load pack as follows. Insert tightly rolled closed cell foam pad, then allow to expand, with double thickness against back panel. Insert quilt so that it fills bottom of pack. If using water bottles, make room for two bottles in bottom of pack, against back panel, with bugbivy and tarp between bottles, to prevent bottles from rubbing against lumbar/sacrum bones. If using water bladder, place bugbivy and tarp on either sides of bladder. Insert tarp pole down side of pack. Remaining items can be loosely arranged at top of pack.
Top of pack closed by twisting neck then wrapping with closure strap and finally tying quick-release knot. For better security, such as when checking pack as baggage during travel, tie secure rather than quick-release knot.
Pack can be washed in either front-loading or top-loading washing machine. For top-loaders especially, be sure to secure straps so they don't get twisted around agitator nor tangled with one another.
Sternum strap keeps shoulder straps away from underarms to prevent being fouled by hard-to-remove underarm smell. If underarm smell nevertheless contaminates pack strap, might be possible to remove using combination of (a) rinsing in stream whenever possible; (b) washing in hotel sink; (c) machine laundering in hot water with white vinegar added during rinse cycle; (d) treating with Mirazyme.
Lower back/bottom panel subject to abrasion from ground and/or body, hence needs abrasion-resistant fabric. Use single piece of fabric for back/bottom panel, since seam between back and bottom would be subject to abrasion from body while wearing pack.
Pack fabric and seams should be able to handle very heavy loads. My experience is that pack becomes comfortable, using shoulder straps only, under 14 kilos (30 lbs). 19 kilos (42 lbs) is my maximum load: 7 kilos of equipment (including pack itself) plus 12 kilos of water and food.
Hip strap only used to keep pack from falling over head when clambering over rocks, not to bear weight, since tightly cinched hip strap interferes with digestion and breathing.
Side-releases have been known to break (had it happen to me for 3/4", seen it happen to others 1.5"), so carry spares. Materials list below does not account for spares. Field repair requires knot rather than hem to secure replacement in place. Sternum strap is extra long to allow such knotting.
Height of 22" gives base capacity of about 55 liters (3400 cuin), or about 41 liters exclusive of ground pad, which requires about 14 liters (840 cuin). Height of 28" gives extended capacity of about 70 liters (4300 cuin), or about 56 liters exclusive of ground pad. However, poncho doesn't fit properly over pack when loaded that high.
Final weight, using fabrics specified below, about 420 grams.

Materials:

1.5 yards sturdy nylon fabric, such as 210D HDPE reinforced gridstop, 4 oz/sqyd (from RipstopByTheRoll.com).
.5 yard abrasion resistant fabric, such as 430 denier packcloth, 7 oz/sqyd (from Seattle Fabrics).
4" by 30" of 3/8" closed cell foam (such as Y-20 from Seattle Fabrics).
12 feet of 3/4" tight-weave nylon webbing.
12 feet of 1" tight-weave nylon webbing.
2 each of 3/4" ladder locks.
2 x 1" dual-pull side-release.
5 feet drawcord, appropriate sized cord-lock.
100% polyester thread, 90/14 universal needles.

Pattern:

backpack pattern

Body:

Double stitching everywhere.
From primary fabric, cut 1 each of upper back and main panels. Cut 4 strap attachments, with opposing orientations for 2 of these 4 pieces.
From abrasion-resistant fabric, cut 1 lower back/bottom panel.
Stitch together upper back panel to lower back/bottom panel to create combined back/bottom panel. Initially 7" overlap between panels, but 1/2" folded under at either edge so that final overlap area 6" high. Overlap area provides extra strong upper attachment point for shoulder straps.
Sew together strap attachment panels with 1/2" seam allowance, right sides facing, leaving long side (which attaches to pack) unsewed. Trim seam allowances to 1/4", zigzag, turn inside out and top-stitch.
Mark 3/4" from sides and bottom of main and back/bottom panels, to guide pinning. Pin then sew together main and back/bottom panels with 3/4" seam allowance. Pin from top down, since curve where back meets bottom may be misleading
Rip side seams starting from bottom of main panel. Insert strap attachment panels, resew. Strap attachment panels longer than necessary, so insert until diagonal flush with side seam, then trim excess after stitching.
Fell back/bottom panel seam towards main panel (making sure to fold strap attachments out of way) and stitch. Extra stitching at bottom of side seams, where maximum stress from strap attachments.
1.25" tunnel at top of body, with 1/2" button-hole in one of side seams. Install cord and cordlock.

Shoulder pads and straps:

Cut 4 shoulder pad case pieces from abrasion resistant fabric, 2 shoulder pad foam pieces. Double-stitch cases with 3/8" seam allowance, except for top end, turn inside out, stuff case with foam, fold over and sew end shut.
Cut/sear 2 x 16" and 2 x 4" of 1.5" webbing, 2 x 4" of 3/4" webbing. Hem ends of 1.5" webbing, thus reducing lengths to 15.5" and 3". Stitch together so that 2" left free. Attach ladder lock to 1.5" strap with 3/4" strap, so that finished strap is 16.5" long. Attach strap to pad using bartacks such that tip of ladder lock even with end of pad. Cut/sear 2 pieces 24" pieces of 1" webbing. Loop around shoulder straps and stitch loop shut. Move this sternum strap down to bartack closest to ladder lock, then add another bartack between shoulder strap and pad just above sternum strap, plus bartack running vertically to hold sternum strap securely against shoulder strap. See photo. In sewing bartacks through shoulder pad, sew only in forward direction: sew forwards, lift presser foot and push material back, depress pressure foot, sew forwards again, etc.
Attach shoulder pads to strap attachment panels of backpack, 4" apart, 19.5" inch from bottom of strap attachment panels, which is about 1" more than my torso length.
Cut/sear 2 pieces 24" long of 3/4" webbing for lower shoulder straps. Attach to strap attachment panels, perpendicular to diagonal side, using triple bartack, with end hemmed under. Feed free ends through ladder locks on shoulder pads. Hem free ends of straps.
Cut/sear 2 pieces 16" long of 1" webbing for hip belt. Attach to strap attachment panels with double bartack, with end hemmed under. Feed straps through 1" dual-pull side-release. Hem free ends of straps.
Cut/sear 1 piece 39" long of 3/4" webbing for closure strap. Attach to center of overlap area using 2" for double bartack, with end hemmed under. Hem free ends of straps.

Finish up:

Apply fray-check to seams and bartacks to prevent unraveling.