Any strap or strap system mainly used for backpack straps and replacement backpack straps, but has many other useful applications as well.
Backpacks have come a long way. Before backpacks there were simple straps to carry your books, some even used belts! In the 1960's backpacks were around, but not yet a big item. Students were found sporting a bag with a single arm strap, or just carrying their books. When backpacks started to get big, they just kept getting bigger and better. Now you can find backpacks that are lightweight and have pockets for everything, MP3's, cell phones, water bottles, etc.
Alternate names include: pack straps, arm straps, carry straps, and shoulder straps. Alternate styles include: Side Release Buckle straps, Universal Carry straps, Plastic Cam straps, Strap Adjuster straps, and Double D-Ring straps.
A backpack strap is often made with Heavyweight Polypropylene webbing. Heavyweight is great for all weather conditions, it has good UV protection, and does not absorb water, making it rot and mildew resistant.
Flat Nylon is also used, which is stronger, has a smoother feel, and has 5x the abrasion resistance of Heavyweight Polypropylene.
The strongest webbing listed here is Polyester webbing, which is much stronger than Nylon, has low stretch, and can be sublimated. Dye sublimation is an imprinting process that results in vibrant, colorfast patterns, logos and also solid colors.
Backpackers usually prefer plastic hardware over metal to keep weight (and cost!) down--especially for a hiker's backpack. The most common hardware for backpacks are: Side Release Buckles, Strap Adjusters, and Slides.
Side Release Buckles are usually sewn on the female half and the male half has slots on the end for cinching and adjusting the webbing--this type is known as "singe adjust." Double Adjust Side Release Buckles have the adjustment slots on both ends and are not sewn to the webbing. Strap Adjusters do just what they say: adjust the length of the strap. Slides help maintain the length you adjusted to.
Other hardware options can include Plastic Cam Buckles, Plastic Keepers, and D-Rings. Cams are used to adjust the strap to the desired length, but unlike Strap Adjusters (which hold the webbing with tension), Cams clamp down on the webbing. The webbing won't work loose over time, and you need to deliberately open the cam to loosen the strap. Keepers are used to keep the loose webbing in place after you've fed it through the buckle, etc. They also are great on webbing belts. D-Rings can be used as something to clip items to on a strap or backpack, or even in place of a buckle if you have two of them on one end of a strap. This would work like a Strap Adjuster--you'd weave the webbing through both D-Rings, and cinch the strap tight.
All webbing has a "breaking strength" and a maximum recommended "working load," and both are based on a "dead lift." Breaking strength refers to how many pounds that webbing can hold before failing, and max work load refers to how much the webbing can lift without the danger of failing. The max recommended work load is a third of the breaking strength. Both of these ratings depend on the type of webbing, the width, and manufacturer. The following are typical ranges: Heavyweight Polypropylene has a breaking strength range of: 450 lbs. to 2,400 lbs., Flat Nylon has a breaking strength range of: 1,400 lbs. to 5,500 lbs., and Polyester has a breaking strength range of: 1,500 lbs. to 10,000 lbs.
When the need arises, there are different ways you can go about backpack repair or backpack strap repair. Taking it in to a professional is one option, but usually spendy.
Doing the repair yourself is less expensive, and can be very rewarding. If you do decide to repair it yourself, you can buy repair kits, but that can be more expensive than need be--you often will have parts you have no use for in a standardized kit. A better way would be to buy loose webbing and hardware that specifically meets your needs.
Some home sewing machines can be used on some webbing, but what if your's can't or you don't have one? There is still no need to take it to a professional.
You could use a sewing awl instead! This tool was once used by sailors to repair canvas, so it will even work on thicker webbing types like Flat Nylon. The Speedy Stitcher sewing awl weighs only 3.14 oz. and come with over 80 feet of waxed thread. They are ideal for field repair--especially on a long hike. Just carry some spare webbing, hardware, and a sewing awl--then you're all set!
The backpack strap is commonly used for backpacks of course, but could substitute for other straps. How about an adjuster strap being used as a cinch strap or a perimeter style strap? That would work great to hold bundled items together, secure your luggage while traveling by wrapping the strap around your suitcase. You can even use an adjuster strap for a plant press! There are other straps that would utilize all of the above applications and more. For example, there are plastic cam straps that are perfect for light duty tie-downs or even a belt.