In the second snippet, foo() captures $i since $i is a lexical. That means the $i in foo() will always refer to the specific SV associated with $i when foo was compiled. When the loop aliases $i to a different SV, it doesn't affect foo.

use Devel::Peek;

my $i;          # Lexical variable

sub foo { Dump($i); }

Dump($i);       # SV ... at 0x226048  \
for $i ( 1 ) {  #                      > same
   foo();       # SV ... at 0x226048  /
   Dump($i);    # SV ... at 0x226d8c
}
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In the first snippet, there is no closure since $i is not a lexical. That means the foo() will always grab the current value of $main::i.

use Devel::Peek;

our $i;         # Package variable

sub foo { Dump($i); }

Dump($i);       # SV ... at 0x226d94
for $i ( 1 ) {
   foo();       # SV ... at 0x226d7c  \ same
   Dump($i);    # SV ... at 0x226d7c  /
}
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