CLAIMS
1. An epoxy resin composition comprising the following constituent elements [A] to [C], wherein the constituent element [C] is the following constituent element [cl] or [c2], and a cured product of the epoxy resin composition has a rubbery state elastic modulus in a dynamic viscoelasticity evaluation of 10 MPa or less:
[A] a phenyl glycidyl ether substituted with a tert-butyl group, a sec-butyl group, an isopropyl group, or a phenyl group;
[B] a bifunctional or higher functional aromatic epoxy resin; and
[C] a hardener:
[cl] an acid anhydride hardener; or [c2] an aliphatic amine.hardener.
2 . The epoxy resin composition according to claim 1, wherein the constituent element [B] is the following constituent element [bl] or [b2] , and the epoxy resin composition has a cure shrinkage rate of 3.5.to 7.0%:
[bl] an optionally substituted diglycidyl aniline; or [b2] tetraglycidyl diaminodiphenylmethane.
3. The epoxy resin composition according to claim 2, comprising 15 to 50 parts by mass of the constituent element

[A] in 100 parts by mass of total epoxy resins.
4 . The epoxy resin composition according to claim 1, wherein the constituent element [B] is the following constituent element [bl] or [b2], and a cured product of the epoxy resin composition has a tensile elongation of 3.5% or less:
[bl] an optionally substituted diglycidyl aniline; or [b2] tetraglycidyl diaminodiphenylmethane.
5. The epoxy resin composition according to claim 4, comprising 20 to 50 parts by mass of the constituent element [A] in 100 parts by mass of total epoxy resins.
6. The epoxy resin composition according to claim 1, having a gel time at 80°C as measured with a rotorless cure meter of 15 to 100 minutes.
7. The epoxy resin composition according to claim 6, comprising 5 to 40 parts by mass of the constituent element [A] in 100 parts by mass of total epoxy resins.
8. The epoxy resin composition according to claim 6 or 7, wherein the constituent element [B] is the following constituent element [bl] or [b2]:
[bl] an optionally substituted diglycidyl aniline; or

[b2] tetraglycidyl diaminodiphenylmethane.
9. The epoxy resin composition according to any one of claims 2 to 5 and 8, wherein the constituent element [B] includes the constituent elements [bl] and [b2] simultaneously.
10. The epoxy resin composition according to any one of claims 1 to 9, wherein the constituent element [A] is a phenyl glycidyl ether substituted with a tert-butyl group or a sec-butyl group.
11. The epoxy resin composition according to any one of claims 2, 3, 6, and 7, comprising two or more components shown as the constituent element [A].
12 . The epoxy resin composition according to any one of claims 1 to 11, wherein the constituent element [C] is the constituent element [cl].
13. The epoxy resin composition according to claim 12, wherein the constituent element [cl] includes a compound having a norbornene backbone or a norbornane backbone.
14. The epoxy resin composition according to claim 12 or 13, comprising an imidazole compound or a tertiary amine compound as an accelerator.

15. The epoxy resin composition according to any one of claims 1 to 11, wherein the constituent element [C] includes the constituent element [c2], which is a cycloalkyldiamine having a substituent on a carbon atom adjacent to a carbon atom having an amino group.
16. The epoxy resin composition according to claim 15, wherein the constituent element [C] further includes an aliphatic polyamine having an alkylene glycol structure as the constituent element [c2] .
17. The epoxy resin composition according to claim 15, wherein the constituent element [C] further includes isophoronediamine as the constituent element [c2].
18 . The epoxy resin composition according to any one of claims 1 to 17, having a viscosity at 25°C of 2000 mPa-s or less.
19. The epoxy resin composition according to claim 18, having a thickening ratio after 90 minutes at 25°C of 4 times or less.
20. The epoxy resin composition according to any one of claims 6 to 8, wherein the cured product of the epoxy resin composition has a compression shear strength in a compression test of 50

to 120 MPa.
21. A fiber reinforced material comprising a cured product of the epoxy resin composition according to any one of claims 1 to 20 and a reinforcing fiber.
22 . A molded article comprising the fiber reinforced material according to claim 21.
23. A pressure vessel comprising the fiber reinforced material according to claim 21.
24. A pressure vessel comprising a liner and a fiber reinforced material layer covering the liner, wherein the fiber reinforced material layer is made from a fiber reinforced material containing a cured product of a thermosetting resin composition and a reinforcing fiber, the 'fiber reinforced material has a glass transition temperature of 95°C or higher, and the pressure vessel has a strain translation rate of 85% or more.
25. The pressure vessel according to claim 24, wherein the cured product of the thermosetting resin composition has a rubbery state elastic modulus obtained by a dynamic viscoelasticity evaluation of 10 MPa or less.

26. The pressure vessel according to claim 24 or 25, wherein
the thermosetting resin composition is an epoxy resin
composition including the following constituent elements [A]
to [C] , the constituent element [B] is the following constituent
element [bl] or [b2] , and the constituent element [C] is at least
one hardener selected from the group consisting of the following
constituent elements [cl] to [c3]:
[A] a phenyl glycidyl ether substituted with any of a tert-butyl group, a sec-butyl group, a sec-butyl group, an isopropyl group, and a phenyl group;
[B] a bifunctional or higher functional aromatic epoxy resin:
[bl] an optionally substituted diglycidyl aniline; or
[b2] tetraglycidyl diaminodiphenylmethane; and
[C] a hardener:
[cl] an acid anhydride hardener;
[c2] an aliphatic amine hardener; and
[c3] an aromatic amine hardener.
27. The pressure vessel according to claim 26, wherein the
constituent element [B] includes the constituent elements [bl]
and [b2] simultaneously.

28. The pressure vessel according to claim 26 or 27, wherein the constituent element [A] is a phenyl glycidyl ether substituted with a tert-butyl group or a sec-butyl group.
29. The pressure vessel according to any one of claims 26 to 28, wherein the constituent element [C] is the constituent element [cl].
30. The pressure vessel according to claim 29, wherein the constituent element [cl] includes a compound having a norbornene backbone or a norbornane backbone.
31. The pressure vessel according to claim 29 or 30, comprising an imidazole compound or a tertiary amine compound as an accelerator.
32. The pressure vessel according to any one of claims 26 to 28, wherein the constituent element [C] includes the constituent element [c2], which is a cycloalkyldiamine having a substituent on a carbon atom adjacent to a carbon atom having an amino group.
33. The pressure vessel according to any one of claims 26 to 28, wherein the constituent element [C] includes the constituent element [c3], which is an aromatic diamine having

a substituent on an ortho position of an amino group.
34. The pressure vessel according to claim 32 or 33, wherein the constituent element [C] further includes an aliphatic polyamine having an alkylene glycol structure as the constituent element [c2]. .
35. The pressure vessel according to claim 32, wherein the constituent element [C] further includes isophoronediamine as the constituent element [c2].