Bendability of strings

I am doing some tutorials for playing acoustic  blues. I know it's not supposed to be a piece of cake but wondering: is string bendability ( aside from one'side finger strenght) a function of the string type, guitar structure, etc. The bends I see on video seem effortless as if the strings are loose. Mine seem to resist bending with their life!!! My Acoustic is an Alvarez cutaway and strings Elixir, nanoweb lights. Thanks

A lot of guitarists, especially blues guitarist, tune down a half or even a full step.  This puts less tension on the strings and makes them easier to bend.  Often you need to set up the guitar for that tuning to avoid string buzz.

The above hit on everything, I think, but to sum it all up in terms of tension (what you are "fighting" to bend a string):
 
Thinner strings have less tension than thicker for the same note.
Shorter scale length requires less tension for the same note.
Tuning down lessens the tension on the strings by default.
 
Acoustic strings are thicker versus electrics for the same notes, so higher tension; but a couple things to also consider:
 
Heavier strings have better sustain and are louder.
More tension (if rigidly mounted) has better sustain.
Altering a guitar from its designed strings may involve tension rod and/or bridge adjustment, so you can use less tension, but possibly at the expense of string buzzing.
 

- String gauge (obviously heavier gauge strings are harder to bend)
- Pitch - as above, some players tune down a half step to 430, which obviously makes things looser than 440.
- Guitar's scale length - shorter scale lengths are easier to bend than longer
- String types:  steel string will be slightly harder than steel / nickel or bronze.  Pure nickel (more applicable to electric guitars than acoustics) will be a bit easier to bend than a combo of nickel / steel.  Nylon is easier to bend than all the others, but I suspect your question is more aimed at steel strings or steel / bronze for acoustics.
- One additional item others haven't noted yet is frets.  I've found higher frets make sting bending quite a bit easier than guitars with lower frets.
- Hand strength.  When I've gone up to a higher string gauge to get a bigger sound, it's taken me several months of playing almost daily to build up the hand strength (and calluses) to be able to play comfortably.

karma1959
 
- Guitar's scale length - shorter scale lengths are easier to bend than longer
 
- One additional item others haven't noted yet is frets.  I've found higher frets make sting bending quite a bit easier than guitars with lower frets.
 
- Hand strength.  When I've gone up to a higher string gauge to get a bigger sound, it's taken me several months of playing almost daily to build up the hand strength (and calluses) to be able to play comfortably.

I don't think the scale length matters too much. And the frets themselves don't make a difference.  I do think that where... in relation to the fixed ends of the strings, you are trying to bend, makes a huge difference. If you bend in the center of the string..... on the "higher" frets, you have much more elasticity in the strings due to being further from their anchor points at the nut and the bridge, and can push it further out of it's line. Closer to the nut end "on the lower frets"  for example, and its harder to push it off that line. I'm sure there's a better explanation that uses calculus and physics to explain it.
 
And physical hand strength matters a lot.

1. AFAIK, most standard acoustic guitars have scale lengths similar to electrics.
 
2. With a few exceptions, the unwound strings in acoustic string sets are identical plain steel strings as used in electric sets. The gauge of course matters, and as discussed above, popular acoustic sets are often heavier gauge.
 
3. String tension is a function of pitch, scale length and the mass of the string, which is determined by the string's gauge, material and construction (wound vs. unwound, etc.).
 
4. String length outside the speaking length of the string (i.e. the length outside of the nut and bridge saddles) can affect the feel of a bend while bending, but ultimately reaching a given pitch is based on the factors listed in #3 above.
 
Pretty much everything else is on the player in terms of proper technique (!), hand strength, etc.

just bend em!@!
 
bend em like you mean it!
commit!
commit!
 
and don't bend sharp, like buddy guy does.
 
(i love that guy)

batsbrew
just bend em!@!
 
bend em like you mean it!
commit!
commit!
 
and don't bend sharp, like buddy guy does.
 
(i love that guy)

Buddy Guy is how I got hooked on Miles Davis!
 
I saw a PBS show in the summer of '65.
 
The first half hour was Mississippi John Hurt sitting alone on stage with a resonator, playing the delta blues like I knew from Gaslight Square in St. Louis. I'd hop the bus after my parents went to sleep and head down to G.S. and get a slice and a Coke for 25 cents and sit outside and listen to the old river blues until the last bus. I was in heaven.
 
The second half hour was this 17 year old kid named Buddy Guy, playing (very) high speed electric blues. Never heard anything like it. Love at first listen.
 
That Christmas, we went to Chicago and stayed with relatives in Elmhurst. Same situation. Adults asleep. I snuck out and took the train into the city to find me some Buddy Guy Chicago blues. Only problem was, it was the 23rd December and cold as s**t and no open windows or doors to hear music. Bummer. I saw one place on the east side of Wells in Old Town that had a line of peeps, so I figured...primo blues!!! Got in line, got in (at 14; not bad ), got a beer (to keep the waitress off my back) and found a place in a back corner.
 
And then the music started. WTF!!! That weren't no blues. WTF!!!
 
Well, long story short, it was Miles on trumpet, Tony Williams on drums, Herbie Hancock on keys, Ron Carter on bass and Wayne Shorter on sax. It was the second night (22nd-23rd December 1965) of their date at the Plugged Nickel. And 40 years later, I got all of it in a CD box set.
 
My mother never understood why I wanted to take up the trumpet. I was supposed to be a classical pianist. Ha ha ha ha ha.
 
But she got even. Once I was off in the Army, she gave away my MIA '63 Fender J bass and my old brownie Fender amp. 
 
EDIT: And my Farfisa mini. 

From looking into flat wounds for my bass, it seems that the same gauge and same material can still produce different stiffness from different companies. The winding process is a factor too. LaBalla flats are stiffer than GHS

When I played guitar in a band, I used ultra-light strings. Ernie Ball Super Slinky. Not for bending, though. It was because I'm a delicate keyboard player and will never need to pound nails with the callouses on my fingers.
 
The downside: I could never put fresh strings on right before a gig because they'd need 3 days to stretch enough to stay in tune. Plus I played a Rickenbacker 12-string, which was never quite in tune anyway.