The DC to avoid the effects of Entrap is constituation based, but the hardness and hit points aren't changed.
Entrap (Ex or Su) The creature has an ability that restricts another creature's movement, usually with a physical attack such as ice, mud, lava, or webs. The target of an entrap attack must make a Fortitude save or become entangled for the listed duration. If a target is already entangled by this ability, a second entrap attack means the target must make a Fortitude save or become helpless for the listed duration. The save DCs are Constitution-based. A target made helpless by this ability is conscious but can take no physical actions (except attempting to break free) until the entrapping material is removed. The target can use spells with only verbal components or spell-like abilities if it can make a DC 20 concentration check. An entangled creature can make a Strength check (at the same DC as the entrap saving throw DC) as a full-round action to break free; the DC for a helpless creature is +5 greater than the saving throw DC. Destroying the entrapping material frees the creature.
As stated in my reply there, the hp does change as the elemental size changes, as does the elemental's con. Therefore, the added con should add to the hp of the entrap.
/cevah
Cevah he is looking for a rules based answer. By the rules that is not how it works. The medium and small mud elemental both have 5 hit point for their entrap ability despite the medium elemental having 2 more constitution.
(DC 12, 10 minutes, hardness 5, hp 5)
entrap (DC 14, 10 minutes, hardness 5, hp 5)
The only thing that changed was the DC.
Cevah he is looking for a rules based answer. By the rules that is not how it works. The medium and small mud elemental both have 5 hit point for their entrap ability despite the medium elemental having 2 more constitution.
(DC 12, 10 minutes, hardness 5, hp 5)entrap (DC 14, 10 minutes, hardness 5, hp 5)The only thing that changed was the DC.
Well, look at the complete set:
Mud Elemental:Size | Hit Points | Con
Huge (Elder) | 15 | 19
Huge (Greater) | 15 | 19
Huge | 15 | 19
Large | 10 | 17
Medium | 5 | 15
Small | 5 | 13
While Con 13 and 15 have the same HP, Con 17 and 19 bump the hp up.
As 13+4 => 17, clearly the hp of the equivalent con elemental is higher.
/cevah
the hp does change as the elemental size changes, as does the elemental's con. Therefore, the added con should add to the hp of the entrap.
Correlation does not imply causation. The entrap HP might be derived from, say, the number of squares the elemental takes up, and have nothing to do with its Constitution.