Introduction: Backpacker's Bottle Cooler
This bottle cooler uses an absorbent sleeve, insulation layer, and waterproof breathable fabric jacket to enable evaporative cooling of a beverage container without the mess of having an exposed wet media. The evaporative cooling water is contained within the waterproof jacket, so the exterior surface is always dry. The water in the absorbent sleeve will slowly evaporate offsetting the heat gain from the surrounding environment. The cooling effect will last as long as the inner absorbent sleeve is kept damp. Each dampening should last 10-12 hours in hot, dry conditions. The effective time can be lengthened by using pre-chilled beverages. Performance is best in dry climates or at high elevation.
Dimensions shown work well for a 1 liter Aquafina water bottle or similar of about 3" diameter by 10" tall. Dimensions shown for 0.5 liter bottle will work for bottles of about 2- 1/2" diameter by 8" tall, typical of Aquafina and Arrowhead. Adjust dimensions to work with your favorite beverage container.
- Waterproof Breathable fabric. (1)
- Absorbent fabric. (2)
- Non-absorbent polyester insulation. (3)
- Nylon cord. (4)
- Cord lock.
- Silicone seam sealant. (5)
- Sewing machine or needle and thread.
- Tape measure or ruler.
- Sharpie marker.
- Disposable glue brush.
- Lighter or candle.
- Small safety pin.
(1) The performance of different waterproof breathable fabrics varies widely in this application. Fabric selection is a tradeoff between cost, weight, durability, leakage resistance, and vapor permeability. Greater vapor permeability increases the evaporative cooling effect; and also reduces how long each recharge of cooling water will last. A fabric called eVent is the most vapor permeable I've tested that is still adequately waterproof. Two-layer or coated waterproof breathable fabrics are acceptable since the inner face is protected, therefore the increased weight of a three-layer fabric is unnecessary.
(2) The performance of different absorbent fabrics varies widely in this application. Fabric selection is a trade-off between cost, weight, durability, water holding capacity, and wickability. Plain cotton terry cloth or polyester microfiber will work, but are heavy for the amount of water they can hold and do not have good wickability. The viscose material used in many "super absorbent" cleaning cloths is very light weight, holds lots of water, and often has good wickability. Cellulose sponge cloths hold a tremendous quantity of water, but become stiff when dry which can impact functionality.
(3) An insulation that does not absorb water is required. I have used Primaloft successfully. Plain polyester batting may work, but has not been tested. The insulation layer has been shown to significantly increase bottle cooler performance under test conditions. The actual performance improvement in field conditions has not been determined.
(4) Any small-diameter draw cord will work.
(5) You can make your own seam sealer by thinning 100% silicone caulk with mineral spirits.
Step 1: Outer Jacket
Cut waterproof breathable fabric; 7-1/2" x 24-1/2" for 1 liter bottle, 6-1/2" x 20" for 0.5 liter bottle.
Fold both corners on one long edge at 45 degrees, about 1", and stitch in place. Hem long edge, opposite the folded corners, about 1/4". Hem short edges about 1/4" then fold again about 1/2" and stitch close to first hem to create a tube for the draw cord.
Step 2: Sew Outer Jacket
Fold right sides together on centerline, straight stitch down each edge about 3/8" from edge. Do not stitch across hem at top edge.
Step 3: Seal Outer Jacket
Apply silicone seam sealer to side stitching of jacket. Use a glue brush to work the sealant into the stitching on one side, allow to cure for about an hour. Apply sealer to the other side and leave undisturbed until complete cured. Turn jacket right side out when seam sealer has cured. Fill with water to test for leaks; dry thoroughly and reseal if necessary.
Step 4: Draw Cord
Cut 20" length of 1/16" - 3/32" diameter nylon cord for 1 liter size, or 16" length for 0.5 liter. Heat seal cord ends in lighter or candle flame. Thread cord through top hem using a small safety pin. Bring ends out through mini cord lock and knot ends of cord.
Step 5: Absorbent Sleeve
Cut absorbent cellulose or viscose fabric; 6-1/2" x 20" for 1 liter, 5-1/2" x 15" for 0.5 liter bottle.
Fold together on centerline across long dimension so it is 6-1/2" x 10", straight stitch down one 10" edge.
Step 6: Add Insulation
Cut polyester insulation; 14" x 9" for 1 liter, 12" x 8" for 0.5 liter.
Fold insulation around stitched side of absorbent fabric with top edges together. Zigzag stitch one layer of each material together along top edge.
Step 7: Finish Inner Sleeve
Straight stitch all four layers together on the other side, about 3/4" from edge. Check bottle fit. Trim about 1/4" from stitching.
Step 8: Assembly Parts
Insert bottle into absorbent sleeve, then insert bottle and sleeve into waterproof jacket.
Step 9: Using the Bottle Cooler
Dampen absorbent sleeve with about 1/2 cup of clean water, rotate to distribute evenly, turn upside down and squeeze out excess water, pull draw cord at top around bottle neck. Fill bottle with beverage. Keep in a well ventilated space for greatest effectiveness. Carry exposed with a shoulder strap or in the mesh pocket of a backpack. The water in the absorbent sleeve will slowly evaporate offsetting the heat gain from the surrounding environment. The cooling effect will last as long as the sleeve is kept damp. Each dampening should last 10-12 hours in hot, dry conditions. The effective time can be lengthened by using pre-chilled beverages.