A PBR two-sided cloth shader that works correctly with Unity's lighting.

!Two-Sided Shader.md

Extended from this article

Two_Sided.shader

/// Created by @cortvi
Shader "Custom/Two sided"
{
	Properties
	{
		// You can learn everything about properties here:
		// https://docs.unity3d.com/Manual/SL-Properties.html
		_Color ("Main Color", Color) = (1,1,1,1)
		_MainTex ("Albedo (RGB)", 2D) = "white" {}
		_Cutoff ("Cutout threshold", Range(0.0,1.0)) = 0.1
		[NoScaleOffset] _SmoothnessMap ("Roughness map (A)", 2D) = "black" {}
		_Smoothness ("Flat roughness", Range(0.0, 1.0)) = 0.0
		[NoScaleOffset][Normal] _BumpMap ("Normal map (RGB)", 2D) = "bump" {}
		_BumpScale ("Normal scale", Float) = 1.0
	}

	SubShader
	{
		Tags { "Queue"="AlphaTest" "RenderType"="TransparentCutout" }

		CGINCLUDE
		// Whatever you write inside here
		// will be included in every pass
		struct Input
		{ float2 uv_MainTex; };

		fixed4 _Color;
		sampler2D _MainTex;
		sampler2D _BumpMap;
		float _BumpScale;
		sampler2D _SmoothnessMap;
		float _Smoothness;

		void surf (Input IN, inout SurfaceOutputStandard o)
		{
			fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
			fixed3 normal = UnpackScaleNormal (tex2D(_BumpMap, IN.uv_MainTex), _BumpScale).xyz;
			fixed smooth = tex2D (_SmoothnessMap, IN.uv_MainTex).a;

			// Feed surface output
			o.Albedo = c.rgb;
			o.Normal = normal;
			o.Metallic = 0.0;
			o.Smoothness = lerp(smooth, 1.0, _Smoothness);
			o.Alpha = c.a;
		}
		ENDCG
		
		Cull Front
		CGPROGRAM
		#pragma surface surf Standard fullforwardshadows vertex:vert alphatest:_Cutoff
		#pragma target 3.0

		void vert (inout appdata_full v)
		{
			v.normal = -v.normal;
		}
		ENDCG
		
		Cull Back
		CGPROGRAM
		#pragma surface surf Standard fullforwardshadows alphatest:_Cutoff
		#pragma target 3.0
		ENDCG
	}

	Fallback "Standard"
}